Method, apparatus, and system for channel access in unlicensed band

ABSTRACT

Disclosed are a method, an apparatus, and a system for performing channel access. In detail, provided are a method including: receiving uplink scheduling information; and when the user equipment has stopped an uplink transmission during the uplink transmission being performed according to the uplink scheduling information, to resume the uplink transmission, performing a second type channel access when a channel sensed by the user equipment is continuously idle after the uplink transmission has been stopped, and performing a first type channel access when the channel sensed by the user equipment is not continuously idle after the uplink transmission has been stopped, wherein the first type channel access comprises performing a random backoff after a channel sensing, and the second type channel access only comprises performing a channel sensing and an apparatus and a system therefor.

TECHNICAL FIELD

The present invention relates to a wireless communication system.

Particularly, the present invention relates to a method, an apparatus,and a system for performing channel access in an unlicensed band.

BACKGROUND ART

In recent years, with an explosive increase of mobile traffic due to thespread of smart devices, it has been difficult to cope with data usagewhich increases for providing a cellular communication service only by aconventional licensed frequency spectrum or LTE-licensed frequency band.

In such a situation, a scheme that uses an unlicensed (alternatively,unauthorized, non-licensed, or license unnecessary) frequency spectrumor LTE-Unlicensed frequency band (e.g., 2.4 GHz band, 5 GHz band, or thelike) for providing the cellular communication service has been devisedas a solution for a spectrum shortage problem.

However, unlike the licensed band in which a communication serviceprovider secures an exclusive frequency use right through a proceduresuch as auction, or the like, in the unlicensed band, multiplecommunication facilities can be used simultaneously without limit whenonly a predetermined level of adjacent band protection regulation isobserved. As a result, when the unlicensed band is used in the cellularcommunication service, it is difficult to guarantee communicationquality at a level provided in the licensed band and an interferenceproblem with a conventional wireless communication device (e.g.,wireless LAN device) using the unlicensed band may occur.

Therefore, a research into a coexistence scheme with the conventionalunlicensed band device and a scheme for efficiently sharing a radiochannel needs to be preferentially made in order to settle an LTEtechnology in the unlicensed band. That is, a robust coexistencemechanism (RCM) needs to be developed in order to prevent a device usingthe LTE technology in the unlicensed band from influencing theconventional unlicensed band device.

DISCLOSURE Technical Problem

The present invention has been made in an effort to provide a method forefficiently transmitting a signal in a wireless communication system, inparticular, a cellular wireless communication system and an apparatustherefor. Further, the present invention has been made in an effort toprovide a method for efficiently transmitting a signal in a specificfrequency band (e.g., unlicensed band) and an apparatus therefor.

Technical objects desired to be achieved in the present invention arenot limited to the aforementioned objects, and other technical objectsnot described above will be apparently understood by those skilled inthe art from the following disclosure.

Technical Solution

The first embodiment of the present invention provides a method forperforming uplink transmission in a specific cell by a user equipment ina wireless communication system including: receiving uplink schedulinginformation; and when the user equipment has stopped an uplinktransmission during the uplink transmission being performed according tothe uplink scheduling information, to resume the uplink transmission,performing a second type channel access when a channel sensed by theuser equipment is continuously idle after the uplink transmission hasbeen stopped, and performing a first type channel access when thechannel sensed by the user equipment is not continuously idle after theuplink transmission has been stopped, wherein the first type channelaccess includes performing a random backoff after a channel sensing, andthe second type channel access only includes performing a channelsensing.

The second embodiment of the present invention provides a user equipmentused in a wireless communication system including: a wirelesscommunication module; and a processor, wherein the processor receivesuplink scheduling information, and when the user equipment has stoppedan uplink transmission during the uplink transmission being performedaccording to the uplink scheduling information, to resume the uplinktransmission, performs a second type channel access when a channelsensed by the user equipment is continuously idle after the uplinktransmission has been stopped, and performs a first type channel accesswhen the channel sensed by the user equipment is not continuously idleafter the uplink transmission has been stopped, wherein the first typechannel access comprises performing a random backoff after a channelsensing, and the second type channel access only comprises performing achannel sensing.

In the first and the second embodiment, the uplink transmission mayinclude a transmission on a plurality of subframes, and stopping, by theuser equipment, the uplink transmission during the uplink transmissionbeing performed may include dropping the uplink transmission in asubframe other than a last subframe on the plurality of subframes.

In the first and the second embodiment, the wireless communicationsystem may include a 3rd generation partnership project (3GPP)-basedwireless communication system, and the first type channel access mayinclude a category-4 listen-before-talk (LBT) and the second typechannel access may include a category-2 LBT.

In the first and the second embodiment, the first type channel accessmay include performing the random backoff using a variable sizecontention window (CW), and the second type channel access may includeperforming the channel sensing for a duration of 25 us without a randombackoff.

In the first and the second embodiment, the specific cell may be anunlicensed cell.

The third embodiment of the present invention provides a method forperforming uplink transmission in multiple carriers by a user equipmentin a wireless communication system including: receiving uplinkscheduling information indicating a first type channel access for acarrier of a first group; receiving uplink scheduling informationindicating a second type channel access for a carrier of a second group;performing a first type channel access only for a specific carrier amongcarriers of the first group and performing a second type channel accessfor remaining carriers; and performing a second type channel accessindicated by the uplink scheduling information for a carrier of a secondgroup, wherein when the first type channel access fails in the specificcarrier, an uplink transmission is dropped only in a carrier of thefirst group among carriers in which the second type channel access isperformed.

The fourth embodiment of the present invention provides a method forperforming uplink transmission in multiple carriers by a user equipmentin a wireless communication system including: receiving uplinkscheduling information indicating a first type channel access for acarrier of a first group; performing a first type channel access onlyfor a specific carrier among carriers of the first group and performinga second type channel access for remaining carriers; and adjusting acontention window size (CWS) for each carrier, wherein receptionresponse information for uplink transmission on the specific carriertransmitted by performing the first type channel access is reflected ina CWS adjustment in the user equipment while reception responseinformation for uplink transmission on remaining carriers in which thefirst type channel access is not performed among carriers of the firstgroup is not reflected in the CWS adjustment in the user equipment.

Advantageous Effects

According to exemplary embodiments of the present invention, providedare a method for efficiently transmitting a signal in a wirelesscommunication system, in particular, a cellular wireless communicationsystem and an apparatus therefor. Further, provided are a method forefficiently transmitting a signal in a specific frequency band (e.g.,unlicensed band) and an apparatus therefor.

Effects to be acquired in the present invention are not limited to theaforementioned effects, and other effects not described above will beapparently understood by those skilled in the art from the followingdisclosure.

DESCRIPTION OF DRAWINGS

In order to help understand the present invention, the accompanyingdrawings which are included as a part of the Detailed Descriptionprovide embodiments of the present invention and describe the technicalmatters of the present invention together with the Detailed Description.

FIG. 1 illustrates physical channels used in a 3rd generationpartnership project (3GPP) system and a general signal transmittingmethod using the physical channels.

FIG. 2 illustrates one example of a radio frame structure used in awireless communication system.

FIG. 3 illustrates one example of a downlink (DL)/uplink (UL) slotstructure in the wireless communication system.

FIG. 4 illustrates a structure of a downlink subframe.

FIG. 5 illustrates a structure of an uplink subframe.

FIG. 6 is a diagram for describing single carrier communication andmulti-carrier communication.

FIG. 7 illustrates an example in which a cross carrier schedulingtechnique is applied.

FIG. 8 illustrates a DL/UL hybrid automatic repeat request (HARQ)procedure in a single cell situation.

FIG. 9 illustrates a licensed assisted access (LAA) service environment.

FIG. 10 illustrates a layout scenario of a user equipment and a basestation in an LAA service environment.

FIG. 11 illustrates a communication scheme that operates in anunlicensed band in the related art.

FIGS. 12 and 13 illustrate a listen-before-talk (LBT) process for DLtransmission.

FIG. 14 illustrates a DL transmission in an unlicensed band.

FIGS. 15 to 17 illustrate a DL transmission process in an unlicensedband.

FIGS. 18 to 22 illustrate a UL transmission process in an unlicensedband.

FIGS. 23 to 27 illustrate a UL multi-carrier transmission according tothe present invention.

FIGS. 28 to 29 are diagrams for explaining a method of resumingtransmission when some transmissions are dropped during multi-subframetransmission.

FIG. 30 illustrates configurations of a user equipment and a basestation according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Terms used in the specification adopt general terms which are currentlywidely used as possible by considering functions in the presentinvention, but the terms may be changed depending on an intention ofthose skilled in the art, customs, and emergence of new technology.Further, in a specific case, there is a term arbitrarily selected by anapplicant and in this case, a meaning thereof will be described in acorresponding description part of the invention. Accordingly, it intendsto be revealed that a term used in the specification should be analyzedbased on not just a name of the term but a substantial meaning of theterm and contents throughout the specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “equal to or more than” or “equal to orless than” based on a specific threshold may be appropriatelysubstituted with “more than” or “less than”, respectively in someexemplary embodiments.

The following technology may be used in various wireless access systems,such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-FDMA(SC-FDMA), and the like. The CDMA may be implemented by a radiotechnology such as universal terrestrial radio access (UTRA) orCDMA2000. The TDMA may be implemented by a radio technology such asglobal system for mobile communications (GSM)/general packet radioservice (GPRS)/enhanced data rates for GSM evolution (EDGE). The OFDMAmay be implemented by a radio technology such as IEEE 802.11(Wi-Fi),IEEE 802.16(WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), and the like.The UTRA is a part of a universal mobile telecommunication system(UMTS). 3^(rd) generation partnership project (3GPP) long term evolution(LTE) is a part of an evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA) and LTE-advanced (A) is an evolvedversion of the 3GPP LTE. 3GPP LTE/LTE-A is primarily described for cleardescription, but technical spirit of the present invention is notlimited thereto.

FIG. 1 illustrates physical channels used in a 3GPP system and a generalsignal transmitting method using the physical channels. A user equipmentreceives information from a base station through downlink (DL) and theuser equipment transmits information through uplink (UL) to the basestation. The information transmitted/received between the base stationand the user equipment includes data and various control information andvarious physical channels exist according to a type/purpose of theinformation transmitted/received between the base station and the userequipment.

When a power of the user equipment is turned on or the user equipmentnewly enters a cell, the user equipment performs an initial cell searchoperation including synchronization with the base station, and the like(S301). To this end, the user equipment receives a primarysynchronization channel (P-SCH) and a secondary synchronization channel(S-SCH) from the base station to synchronize with the base station andobtain information including a cell ID, and the like. Thereafter, theuser equipment receives a physical broadcast channel from the basestation to obtain intra-cell broadcast information. The user equipmentreceives a downlink reference signal (DL RS) in an initial cell searchstep to verify a downlink channel state.

The user equipment that completes initial cell search receives aphysical downlink control channel (PDCCH) and a physical downlink sharedchannel (PDSCH) depending on information loaded on the PDCCH to obtainmore detailed system information (S302).

When there is no radio resource for initially accessing the base stationor signal transmission, the user equipment may perform a random accessprocedure (RACH procedure) to the base station (S303 to S306). To thisend, the user equipment may transmit a preamble through a physicalrandom access channel (PRACH) (S303) and receive a response message tothe preamble through the PDCCH and the PDSCH corresponding thereto(S304). In the case of a contention based RACH, a contention resolutionprocedure may be additionally performed.

Thereafter, the user equipment may receive the PDCCH/PDSCH (S307) andtransmit a physical uplink shared channel (PUSCH)/physical uplinkcontrol channel (PUCCH) (S308) as a general procedure. The userequipment receives downlink control information (DCI) through the PDCCH.The DCI includes control information such as resource allocationinformation to the user equipment and a format varies depending on a usepurpose. The control information which the user equipment transmits tothe base station is designated as uplink control information (UCI). TheUCI includes an acknowledgement/negative acknowledgement (ACK/NACK), achannel quality indicator (CQI), a precoding matrix index (PMI), a rankindicator (RI), and the like. The UCI may be transmitted through thePUSCH and/or PUCCH.

FIG. 2 illustrates one example of a radio frame structure used in awireless communication system. FIG. 2A illustrates a frame structure forfrequency division duplex (FDD) and FIG. 2B illustrates a framestructure for time division duplex (TDD).

Referring to FIG. 2, a radio frame may have a length of 10 ms (307200Ts) and be constituted by 10 subframes (SFs). Ts represents a samplingtime and is expressed as Ts=1/(2048*15 kHz). Each subframe may have alength of 1 ms and be constituted by 2 slots. Each slot has a length of0.5 ms. A time for transmitting one subframe is defined as atransmission time interval (TTI). A time resource may be distinguishedby radio frame numbers/indexes, subframe numbers/indexes #0 to #9, andslot numbers/indexes #0 to #19.

The radio frame may be configured differently according to a duplexmode. In an FDD mode, downlink transmission and uplink transmission aredistinguished by a frequency and the radio frame includes only one of adownlink subframe and an uplink subframe with respect to a specificfrequency band. In a TDD mode, the downlink transmission and the uplinktransmission are distinguished by a time and the radio frame includesboth the downlink subframe and the uplink subframe with respect to aspecific frequency band.

FIG. 3 illustrates a structure of a downlink/uplink slot.

Referring to FIG. 3, the slot includes a plurality of orthogonalfrequency divisional multiplexing (OFDM) symbols in a time domain and aplurality of resource blocks (RBs) in a frequency domain. The OFDMsymbol also means one symbol period. The OFDM symbol may be called anOFDMA symbol, a single carrier frequency division multiple access(SC-FDMA) symbol, or the like according to a multi-access scheme. Thenumber of OFDM symbols included in one slot may be variously modifiedaccording to the length of a cyclic prefix (CP). For example, in thecase of a normal CP, one slot includes 7 OFDM symbols and in the case ofan extended CP, one slot includes 6 OFDM symbols. The RB is defined asN^(DL/UL) _(symb) (e.g., 7) continuous OFDM symbols in the time domainand N^(RB) _(sc) (e.g., 12) continuous subcarriers in the frequencydomain. A resource constituted by one OFDM symbol and one subcarrier isreferred to as a resource element (RE) or a tone. One RB is constitutedby N^(DL/UL) _(symb)*N^(RB) _(sc) resource elements.

The resource of the slot may be expressed as a resource grid constitutedby N^(DL/UL) _(RB)*N^(RB) _(sc) subcarriers and N^(DL/UL) _(symb) OFDMsymbols. Each RE in the resource grid is uniquely defined by an indexpair (k, 1) for each slot. k represents an index given with 0 toN^(DL/UL) _(RB)*N^(RB) _(sc)−1 in the frequency domain and 1 representsan index given with 0 to N^(DL/UL) _(symb)−1 in the time domain. Herein,N^(DL) _(RB) represents the number of resource blocks (RBs) in thedownlink slot and N^(UL) _(RB) represents the number of RBs in the ULslot. N^(DL) _(RB) and N^(UL) _(RB) depend on a DL transmissionbandwidth and a UL transmission bandwidth, respectively. N^(DL) _(symb)represents the number of symbols in the downlink slot and N^(UL) _(symb)represents the number of symbols in the UL slot. N^(RB) _(sc) representsthe number of subcarriers constituting one RB. One resource grid isprovided per antenna port.

FIG. 4 illustrates a structure of a downlink subframe.

Referring to FIG. 4, the subframe may be constituted by 14 OFDM symbols.First 1 to 3 (alternatively, 2 to 4) OFDM symbols are used as a controlregion and the remaining 13 to 11 (alternatively, 12 to 10) OFDM symbolsare used as a data region according to subframe setting. R1 to R4represent reference signals for antenna ports 0 to 3. Control channelsallocated to the control region include a physical control formatindicator channel (PCFICH), a physical hybrid-ARQ indicator channel(PHICH), a physical downlink control channel (PDCCH), and the like. Datachannels allocated to the data region include the PDSCH, and the like.When an enhanced PDCCH (EPDCCH) is set, the PDSCH and the EPDCCH aremultiplexed by frequency division multiplexing (FDM) in the data region.

The PDCCH as the physical downlink control channel is allocated to firstn OFDM symbols of the subframe. n as an integer of 1 (alternatively, 2)or more is indicated by the PCFICH. The PDCCH announces informationassociated with resource allocation of a paging channel (PCH) and adownlink-shared channel (DL-SCH) as transmission channels, an uplinkscheduling grant, HARQ information, and the like to each user equipmentor user equipment group. Data (that is, transport block) of the PCH andthe DL-SCH are transmitted through the PDSCH. Each of the base stationand the user equipment generally transmit and receive data through thePDSCH except for specific control information or specific service data.

Information indicating to which user equipment (one or a plurality ofuser equipments) the data of the PDSCH is transmitted, informationindicating how the user equipments receive and decode the PDSCH data,and the like are transmitted while being included in the PDCCH/EPDCCH.For example, it is assumed that the PDCCH/EPDCCH is CRC-masked with aradio network temporary identity (RNTI) called “A” and informationregarding data transmitted by using a radio resource (e.g., frequencylocation) called “B” and a DCI format called “C”, that is, transmissionformat information (e.g., transport block size, modulation scheme,coding information, and the like) is transmitted through a specificsubframe. In this case, a user equipment in the cell monitors thePDCCH/EPDCCH by using the RNTI information thereof and when one or moreuser equipments having the “A” RNTI are provided, the user equipmentsreceive the PDCCH/EPDCCH and receive the PDSCH indicated by “B” and “C”through information on the received PDCCH/EPDCCH.

FIG. 5 illustrates a structure of an uplink subframe.

Referring to FIG. 5, the subframe may be divided into the control regionand the data region in the frequency domain. The PUCCH is allocated tothe control region and carries the UCI. The PUSCH is allocated to thedata region and carries user data.

The PUCCH may be used to transmit the following control information.

-   -   Scheduling Request (SR): Information used to request a UL-SCH        resource. The SR is transmitted by using an on-off keying (OOK)        scheme.    -   HARQ-ACK: Response to the PDCCH and/or response to a downlink        data packet (e.g., codeword) on the PDSCH. The codeword is an        encoded format of the transport block. The HARQ-ACK indicates        whether the PDCCH or PDSCH is successfully received. The        HARQ-ACK response includes a positive ACK (simply, ACK), a        negative ACK (NACK), discontinuous transmission (DTX), or the        NACK/DTX. The DTX represents a case in which the user equipment        misses the PDCCH (alternatively, semi-persistent scheduling        (SPS) PDSCH) and the NACK/DTX means the NACK or DTX. The        HARQ-ACK is mixedly used with the HARQ-ACK/NACK and the        ACK/NACK.    -   Channel State Information (CSI): Feed-back information regarding        the downlink channel. Multiple input multiple output (MIMO)        related feed-back information includes the RI and the PMI.

Table 1 shows the relationship between a PUCCH format and the UCI.

TABLE 1 PUCCH Format Uplink control information (UCI) Format 1Scheduling request (SR) (non-modulated waveform) Format 1a 1-bit HARQACK/NACK (SR existence/non-existence) Format 1b 2-bit HARQ ACK/NACK (SRexistence/non-existence) Format 2 CSI (20 coded bits) Format 2 CSI and 1or 2-bit HARQ ACK/NACK (20 bits) (corresponding to only extended CP)Format 2a CSI and 1-bit HARQ ACK/NACK (20 + 1 coded bits) Format 2b CSIand 2-bit HARQ ACK/NACK (20 + 2 coded bits) Format 3 HARQ ACK/NACK + SR(48 coded bits) (LTE-A)

Hereinafter, carrier aggregation will be described. The carrieraggregation means a method in which the wireless communication systemuses a plurality of frequency blocks as one large logical frequency bandin order to use a wider frequency band. When a whole system band isextended by the carrier aggregation, a frequency band used forcommunication with each user equipment is defined by a component carrier(CC) unit.

FIG. 6 is a diagram for describing single carrier communication andmulti-carrier communication. FIG. 6(a) illustrates a subframe structureof a single carrier and FIG. 6(b) illustrates a subframe structure ofmulti-carriers which are carrier-aggregated.

Referring to FIG. 6(a), in a single carrier system, the base station andthe user equipment perform data communication through one DL band andone UL band corresponding thereto. The DL/UL band is divided into aplurality of orthogonal subcarriers and each frequency band operates atone carrier frequency. In the FDD, the DL and UL bands operate atdifferent carrier frequencies, respectively and in the TDD, the DL andUL bands operate at the same carrier frequency. The carrier frequencymeans a center frequency of the frequency band.

Referring to FIG. 6(b), the carrier aggregation is distinguished from anOFDM system that performs DL/UL communication in a base frequency banddivided into a plurality of subcarriers by using one carrier frequency,in that the carrier aggregation performs DL/UL communication by using aplurality of carrier frequencies. Referring to FIG. 6(b), three 20 MHzCCs are gathered in each of the UL and the DL to support a bandwidth of60 MHz. The CCs may be adjacent to each other or non-adjacent to eachother in the frequency domain. For convenience, FIG. 6(b) illustrates acase in which a bandwidth of a UL CC and a bandwidth of a DL CC are thesame as each other and symmetric to each other, but the bandwidths ofthe respective CCs may be independently decided. Further, asymmetriccarrier aggregation in which the number of UL CCs and the number of DLCCs are different from each other is also available. The DL/UL CC(s) areindependently allocated/configured for each user equipment and the DL/ULCC(s) allocated/configured to the user equipment are designated asserving UL/DL CC(s) of the corresponding user equipment.

The base station may activate some or all of serving CCs of the userequipment or deactivate some CCs. When the base station allocates theCC(s) to the user equipment, if the CC allocation to the user equipmentis wholly reconfigured or if the user equipment does not hand over, atleast one specific CC among the CC(s) configured with respect to thecorresponding user equipment is not deactivated. A specific CC which isalways activated is referred to as a primary CC (PCC) and a CC which thebase station may arbitrarily activate/deactivate is referred to as asecondary CC (SCC). The PCC and the SCC may be distinguished based onthe control information. For example, specific control information maybe set to be transmitted/received only through a specific CC and thespecific CC may be referred to as the PCC and remaining CC(s) may bereferred to as SCC(s). The PUCCH is transmitted only on the PCC.

In 3GPP, a concept of the cell is used in order to manage the radioresource. The cell is defined as a combination of the DL resource andthe UL resource, that is, a combination of the DL CC and the UL CC. Thecell may be configured by the DL resource only or the combination of theDL resource and the UL resource. When the carrier aggregation issupported, a linkage between the carrier frequency of the DL resource(alternatively, DL CC) and the carrier frequency of the UL resource(alternatively, UL CC) may be indicated by system information. Forexample, the combination of the DL resource and the UL resource may beindicated by a system information block type 2 (SIB2) linkage. Thecarrier frequency means a center frequency of each cell or CC. A cellcorresponding to the PCC is referred to as the primary cell (PCell) anda cell corresponding to the SCC is referred to as the secondary cell(SCell). A carrier corresponding to the PCell is a DL PCC in thedownlink and a carrier corresponding to the PCell is a UL PCC in theuplink. Similarly, a carrier corresponding to the SCell is a DL SCC inthe downlink and a carrier corresponding to the SCell is a UL SCC in theuplink. According to a user equipment capability, the serving cell(s)may be constituted by one PCell and 0 or more SCells. For a userequipment which is in an RRC_CONNECTED state, but does not have anyconfiguration for the carrier aggregation or does not support thecarrier aggregation, only one serving cell constituted by only the PCellis present.

FIG. 7 illustrates an example in which cross carrier scheduling isapplied. When the cross carrier scheduling is configured, a controlchannel transmitted through a first CC may schedule a data channeltransmitted through the first CC or a second CC by using a carrierindicator field (CIF). The CIF is included in the DCI. In other words, ascheduling cell is configured, and a DL grant/UL grant transmitted in aPDCCH area of the scheduling cell schedules the PDSCH/PUSCH of ascheduled cell. That is, a search space for a plurality of componentcarriers is present in the PDCCH area of the scheduling cell. The PCellmay be basically the scheduling cell and a specific SCell may bedesignated as the scheduling cell by an upper layer.

In FIG. 7, it is assumed that three DL CCs are aggregated. Herein, DLcomponent carrier #0 is assumed as the DL PCC (alternatively, PCell) andDL component carrier #1 and DL component carrier #2 are assumed as theDL SCC (alternatively, SCell). Further, it is assumed that the DL PCC isset as a PDCCH monitoring CC. When the CIF is disabled, the respectiveDL CCs may transmit only the PDCCH that schedules the PDSCH thereofwithout the CIF according to an LTE PDCCH rule (non-cross carrierscheduling or self-carrier scheduling). On the contrary, when the CIF isenabled by UE-specific (alternatively, UE-group-specific orcell-specific) upper layer signaling, a specific CC (e.g., DL PCC) maytransmit the PDCCH scheduling the PDSCH of DL CC A and the PDCCHscheduling the PDSCH of another CC by using the CIF (cross-carrierscheduling). On the contrary, in another DL CC, the PDCCH is nottransmitted.

FIG. 8 illustrates a DL/UL HARQ procedure for a single cell situation.FIG. 8(a) illustrates a DL HARQ procedure, and FIG. 8(b) illustrates aUL HARQ procedure. In the case of DL HARQ procedure, ACK/NACK (A/N) for(i) a PDSCH scheduled by a PDCCH, (ii) a PDSCH (i.e., SPS PDSCH) withouta corresponding PDCCH, and (iii) a PDCCH indicating the SPS release arefed back. In the case of UL HARQ procedure, ACK/NACK (A/N) for (i) aPUSCH scheduled by a PDCCH and (ii) a PUSCH (i.e., SPS PUSCH) without acorresponding PDCCH are fed back. A PDCCH includes an EPDCCH.

Referring to FIG. 8(a), a user equipment receives a PDCCH(alternatively, EPDCCH) in a subframe # n-k (S802) and receives a PDSCHindicated by the PDCCH in the same subframe (S804). The PDCCH transmitsscheduling information (that is, DL grant) and the PDSCH transmits oneor a plurality of (e.g., two) transport blocks (TBs) (alternatively,codeword (CW)) according to a transmission mode. Thereafter, the userequipment may transmit an ACK/NACK for the PDSCH (that is, transportblock) in a subframe # n (S806). ACK/NACK 1 bit may be transmitted inresponse to a single transport block and ACK/NACK 2 bits may betransmitted in response to two transport blocks. The ACK/NACK isbasically transmitted through the PUCCH, but when the PUSCH istransmitted in the subframe # n, the ACK/NACK may be transmitted throughthe PUSCH. k represents a time interval between the DL subframe and theUL subframe. In the FDD, k=4 and in the TDD, k may be given by adownlink association set index (DASI). The ACK/NACK means the HARQ-ACK.The HARQ-ACK response includes ACK, NACK, DTX, and NACK/DTX.

Referring to FIG. 8(b), the user equipment receives a PDCCH(alternatively, EPDCCH) in a subframe # n-k1 (S812) and transmits aPUSCH indicated by the PDCCH in the subframe # n (S814). The PDCCHtransmits scheduling information (that is, UL grant), and the PUSCHtransmits one or a plurality (e.g., two) of transport blocks (TBs)(alternatively, codewords (CW)) according to a transmission mode.Thereafter, the user equipment receives reception response informationfor the PUSCH (i.e., the transport block) in a subframe # n+k2 through aPHICH or UL grant (S816). The UL grant includes new data indicator (NDI)for each TB. In addition, the NDI indicates a new data transmission orindicates retransmission of the TB of the previous PUSCH according tothe toggle. For example, if the NDI is toggled from the NDI value of theprevious UL grant, the NDI indicates the new data transmission, andotherwise the NDI indicates retransmission of the TB of the previousPUSCH. k1/k2 indicates a time interval between the DL subframe and theUL subframe. In the FDD, k1=k2=4, and in the TDD, k1/k2 depends on theTDD UL-DL configuration.

When a plurality of cells are configured for the user equipment,ACK/NACK information may be transmitted by using PUCCH format 3 or achannel selection scheme based on PUCCH format 1b.

An ACK/NACK payload for PUCCH format 3 is configured for each cell andthereafter, concatenated according to a cell index order. The ACK/NACKpayload is configured with respect to all cells configured to the userequipment regardless of actual data transmission in each cell. Each bitin the ACK/NACK payload indicates HARQ-ACK feed-back for thecorresponding transport block (alternatively, codeword). The HARQ/ACKfeed-back indicates ACK or NACK, and DTX is processed as the NACK. TheNACK and the DTX have the same HARQ-ACK feed-back value. If necessary,the base station may distinguish the NACK and the DTX by usinginformation on the control channel which the base station transmits tothe user equipment.

The channel selection scheme based on the PUCCH format 1b may be set fortransmitting the ACK/NACK when two cells are aggregated. In the channelselection scheme based on the PUCCH format 1b, ACK/NACK responses to theplurality of transport blocks (alternatively, codewords) are identifiedby a combination of a PUCCH resource index and a bit value.

Table 2 shows mapping between HARQ-ACK(j) and the transport block (TB)of each cell in the channel selection scheme based on the PUCCH format1b. Tables 3 to 5 show mapping of ACK, NACK, DTX, and NACK/DTX when A=2to 4, respectively. The user equipment selects one PUCCH resourcecorresponding to an HARQ-ACK set from A PUCCH resources and transmits a2-bit value corresponding to the HARQ-ACK set by using the selectedPUCCH resource. The DTX is transmitted singly or as the NACK/DTX. Whenthe NACK/DTX is transmitted, if necessary, the base station maydistinguish the NACK and the DTX by using the information on the controlchannel which the base station transmits to the user equipment.

TABLE 2 HARQ-ACK(j) A HARQ-ACK(0) HARQ-ACK(1) HARQ-ACK(2) HARQ-ACK(3) 2TB1 PRIMARY TB1 NA NA CELL SECONDARY CELL 3 TB1 SERVING TB2 SERVING TB1SERVING NA CELL1 CELL1 CELL2 4 TB1 PRIMARY TB2 PRIMARY TB1 TB2 CELL CELLSECONDARY SECONDARY CELL CELL

TABLE 3 HARQ-ACK(0) HARQ-ACK(1) n_(PUCCH) ⁽¹⁾ b(0)b(1) ACK ACKn_(PUCCH, 1) ⁽¹⁾ 1, 1 ACK NACK/DTX n_(PUCCH, 0) ⁽¹⁾ 1, 1 NACK/DTX ACKn_(PUCCH, 1) ⁽¹⁾ 0, 0 NACK NACK/DTX n_(PUCCH, 0) ⁽¹⁾ 0, 0 DTX NACK/DTXNO TRANSMISSION

TABLE 4 HARQ-ACK(0) HARQ-ACK(1) HARQ-ACK(2) n_(PUCCH) ⁽¹⁾ b(0)b(1) ACKACK ACK n_(PUCCH, 1) ⁽¹⁾ 1, 1 ACK NACK/DTX ACK n_(PUCCH, 1) ⁽¹⁾ 1, 0NACK/DTX ACK ACK n_(PUCCH, 1) ⁽¹⁾ 0, 1 NACK/DTX NACK/DTX ACKn_(PUCCH, 2) ⁽¹⁾ 1, 1 ACK ACK NACK/DTX n_(PUCCH, 0) ⁽¹⁾ 1, 1 ACKNACK/DTX NACK/DTX n_(PUCCH, 0) ⁽¹⁾ 1, 0 NACK/DTX ACK NACK/DTXn_(PUCCH, 0) ⁽¹⁾ 0, 1 NACK/DTX NACK/DTX NACK n_(PUCCH, 2) ⁽¹⁾ 0, 0 NACKNACK/DTX DTX n_(PUCCH, 0) ⁽¹⁾ 0, 0 NACK/DTX NACK DTX n_(PUCCH, 0) ⁽¹⁾ 0,0 DTX DTX DTX NO TRANSMISSION

TABLE 5 HARQ-ACK(0) HARQ-ACK(1) HARQ-ACK(2) HARQ-ACK(3) n_(PUCCH) ⁽¹⁾b(0)b(1) ACK ACK ACK ACK n_(PUCCH, 1) ⁽¹⁾ L 1 ACK NACK/DTX ACK ACKn_(PUCCH, 2) ⁽¹⁾ 0, 1 NACK/DTX ACK ACK ACK n_(PUCCH, 1) ⁽¹⁾ 0, 1NACK/DTX NACK/DTX ACK ACK n_(PUCCH, 3) ⁽¹⁾ 1, 1 ACK ACK ACK NACK/DTXn_(PUCCH, 1) ⁽¹⁾ 1, 0 ACK NACK/DTX ACK NACK/DTX n_(PUCCH, 2) ⁽¹⁾ 0, 0NACK/DTX ACK ACK NACK/DTX n_(PUCCH, 1) ⁽¹⁾ 0, 0 NACK/DTX NACK/DTX ACKNACK/DTX n_(PUCCH, 3) ⁽¹⁾ 1, 0 ACK ACK NACK/DTX ACK n_(PUCCH, 2) ⁽¹⁾ 1,1 ACK NACK/DTX NACK/DTX ACK n_(PUCCH, 2) ⁽¹⁾ 1, 0 NACK/DTX ACK NACK/DTXACK n_(PUCCH, 3) ⁽¹⁾ 0, 1 NACK/DTX NACK/DTX NACK/DTX ACK n_(PUCCH, 3)⁽¹⁾ 0, 0 ACK ACK NACK/DTX NACK/DTX n_(PUCCH, 0) ⁽¹⁾ 1, 1 ACK NACK/DTXNACK/DTX NACK/DTX n_(PUCCH, 0) ⁽¹⁾ 1, 0 NACK/DTX ACK NACK/DTX NACK/DTXn_(PUCCH, 0) ⁽¹⁾ 0, 1 NACK/DTX NACK NACK/DTX NACK/DTX n_(PUCCH, 0) ⁽¹⁾0, 0 NACK NACK/DTX NACK/DTX NACK/DTX n_(PUCCH, 0) ⁽¹⁾ 0, 0 DTX DTXNACK/DTX NACK/DTX NO TRANSMISSION

Example: CWS Adjustment Scheme for Random Back-Off in Unlicensed Band

FIG. 9 illustrates a licensed assisted access (LAA) service environment.

Referring to FIG. 9, a service environment may be provided to a user, inthe service environment, an LTE technology (11) in a conventionallicensed band and LTE-unlicensed (LTE-U) or LAA which is an LTEtechnology (12) in an unlicensed band, which has been actively discussedmay be connected to each other. For example, the LTE technology (11) inthe licensed band and the LTE technology (12) in the unlicensed band inthe LAA environment may be integrated by using a technology such ascarrier aggregation, or the like, which may contribute to extension of anetwork capacity. Further, in an asymmetric traffic structure in whichthe amount of downlink data is more than that of uplink data, the LAAmay provide an optimized LTE service according to various requirementsor environments. For convenience, the LTE technology in the licensed(alternatively, authorized or permitted) band is referred to asLTE-licensed (LTE-L) and the LTE technology in the unlicensed(alternatively, unauthorized, non-licensed, license-unnecessary) band isreferred to as LTE-unlicensed (LTE-U) or LAA.

FIG. 10 illustrates a layout scenario of a user equipment and a basestation in an LAA service environment. A frequency band targeted by theLAA service environment has a short wireless communication reachdistance due to a high-frequency characteristic. By considering this,the layout scenario of the user equipment and the base station in anenvironment in which the conventional LTE-L service and the LAA servicecoexist may be an overlay model and a co-located model.

In the overlay model, a macro base station may perform wirelesscommunication with an X UE and an X′ UE in a macro area (32) by using alicensed carrier and be connected with multiple radio remote heads(RRHs) through an X2 interface. Each RRH may perform wirelesscommunication with an X UE or an X′ UE in a predetermined area (31) byusing an unlicensed carrier. The frequency bands of the macro basestation and the RRH are different from each other not to interfere witheach other, but data needs to be rapidly exchanged between the macrobase station and the RRH through the X2 interface in order to use theLAA service as an auxiliary downlink channel of the LTE-L servicethrough the carrier aggregation.

In the co-located model, a pico/femto base station may perform thewireless communication with a Y UE by using both the licensed carrierand the unlicensed carrier. However, it may be limited that thepico/femto base station uses both the LTE-L service and the LAA serviceto downlink transmission. A coverage (33) of the LTE-L service and acoverage (34) of the LAA service may be different according to thefrequency band, transmission power, and the like.

When LTE communication is performed in the unlicensed band, conventionalequipments (e.g., wireless LAN (Wi-Fi) equipments) which performcommunication in the corresponding unlicensed band may not demodulate anLTE-U message or data and determine the LTE-U message or data as a kindof energy to perform an interference avoidance operation by an energydetection technique. That is, when energy corresponding to the LTE-Umessage or data is lower than −62 dBm or certain energy detection (ED)threshold value, the wireless LAN equipments may perform communicationby disregarding the corresponding message or data. As a result, thatuser equipment which performs the LTE communication in the unlicensedband may be frequently interfered by the wireless LAN equipments.

Therefore, a specific frequency band needs to be allocated or reservedfor a specific time in order to effectively implement an LTE-Utechnology/service. However, since peripheral equipments which performcommunication through the unlicensed band attempt access based on theenergy detection technique, there is a problem in that an efficientLTE-U service is difficult. Therefore, a research into a coexistencescheme with the conventional unlicensed band device and a scheme forefficiently sharing a radio channel needs to be preferentially made inorder to settle the LTE-U technology. That is, a robust coexistencemechanism in which the LTE-U device does not influence the conventionalunlicensed band device needs to be developed.

FIG. 11 illustrates a communication scheme (e.g., wireless LAN) thatoperates in an unlicensed band in the related art. Since most devicesthat operate in the unlicensed band operate based on listen-before-talk(LBT), a clear channel assessment (CCA) technique that senses a channelbefore data transmission is performed.

Referring to FIG. 11, a wireless LAN device (e.g., AP or STA) checkswhether the channel is busy by performing carrier sensing beforetransmitting data. When a predetermined strength or more of radio signalis sensed in a channel to transmit data, it is determined that thecorresponding channel is busy and the wireless LAN device delays theaccess to the corresponding channel. Such a process is referred to asclear channel evaluation and a signal level to decide whether the signalis sensed is referred to as a CCA threshold. Meanwhile, when the radiosignal is not sensed in the corresponding channel or a radio signalhaving a strength smaller than the CCA threshold is sensed, it isdetermined that the channel is idle.

When it is determined that the channel is idle, a terminal having datato be transmitted performs a back-off procedure after a defer period(e.g., arbitration interframe space (AIFS), PCF IFS (PIFS), or thelike). The defer period means a minimum time when the terminal needs towait after the channel is idle. The back-off procedure allows theterminal to further wait for a predetermined time after the deferperiod. For example, the terminal stands by while decreasing a slot timefor slot times corresponding to a random number allocated to theterminal in the contention window (CW) during the channel is in an idlestate, and a terminal that completely exhausts the slot time may attemptto access the corresponding channel.

When the terminal successfully accesses the channel, the terminal maytransmit data through the channel. When the data is successfullytransmitted, a CW size (CWS) is reset to an initial value (CWmin). Onthe contrary, when the data is unsuccessfully transmitted, the CWSincreases twice. As a result, the terminal is allocated with a newrandom number within a range which is twice larger than a previousrandom number range to perform the back-off procedure in a next CW. Inthe wireless LAN, only an ACK is defined as receiving responseinformation to the data transmission. Therefore, when the ACK isreceived with respect to the data transmission, the CWS is reset to theinitial value and when feed-back information is not received withrespect to the data transmission, the CWS increases twice.

As described above, since most communications in the unlicensed band inthe related art operate based on the LBT, the LTE also considers the LBTin the LAA for coexistence with the conventional device. In detail, inthe LTE, the channel access method on the unlicensed band may be dividedinto 4 following categories according to the presence/an applicationscheme of the LBT.

-   -   Category 1 (cat-1): No LBT        -   An LBT procedure by a Tx entity is not performed.    -   Category 2 (cat-2): LBT without random back-off        -   A time interval (e.g., 25 us) in which the channel needs to            be sensed in an idle state before the Tx entity performs a            transmission on the channel is decided. The random back-off            is not performed. This may be referred to as a type 2            channel access.    -   Category 3 (cat-3): LBT with random back-off with a CW of fixed        size        -   LBT method that performs random back-off by using a CW of a            fixed size. The Tx entity has a random number N in the CW            and the CW size is defined by a minimum/maximum value of N.            The CW size is fixed. The random number N is used to decide            the time interval in which the channel needs to be sensed in            an idle state before the Tx entity performs a transmission            on the channel.    -   Category 4 (cat-4): LBT with random back-off with a CW of        variable size        -   LBT method that performs the random back-off by using a CW            of a variable size. The Tx entity has the random number N in            the CW and the CW size is defined by the minimum/maximum            value of N. The Tx entity may change the CW size at the time            of generating the random number N. The random number N is            used to decide the time interval in which the channel needs            to be sensed in an idle state before the Tx entity performs            a transmission on the channel. This may be referred to as a            type 1 channel access.

FIGS. 12 and 13 illustrate a DL transmission process based on thecategory 4 LBT. The category 4 LBT may be used to guarantee fair channelaccess with Wi-Fi. Referring to FIGS. 12 and 13, the LBT processincludes initial CCA (ICCA) and extended CCA (ECCA). In the ICCA, therandom back-off is not performed and in the ECCA, the random back-off isperformed by using the CW of the variable size. The ICCA is applied tothe case in which the channel is idle when signal transmission isrequired and the ECCA is applied to the case in which the channel isbusy when the signal transmission is required or DL transmission isperformed just before. Although the following description is based onthe DL transmission, it is also applicable to the UL transmission. Inthe case of UL transmission, the base station is replaced with a userequipment in the following description.

Referring to FIG. 12, a downlink transmission process based on thecategory 4 LBT, that is, the Type 1 channel access may be performed asfollows.

Initial CCA

-   -   S1202: The base station verifies that the channel is idle.    -   S1204: The base station verifies whether the signal transmission        is required. When the signal transmission is not required, the        process returns to S1202 and when the signal transmission is        required, the process proceeds to S1206.    -   S1206: The base station verifies whether the channel is idle for        an ICCA defer period (B_(CCA)). The ICCA defer period is        configurable. As an implementation example, the ICCA defer        period may be constituted by an interval of 16 μs and n        consecutive CCA slots. Herein, n may be a positive integer and        one CCA slot interval may be 9 μs. The number of CCA slots may        be configured differently according to a QoS class. The ICCA        defer period may be set to an appropriate value by considering a        defer period (e.g., DIFS or AIFS) of Wi-Fi. For example, the        ICCA defer period may be 34 us. When the channel is idle for the        ICCA defer period, the base station may perform the signal        transmitting process (S1208). When it is determined that the        channel is busy during the ICCA defer period, the process        proceeds to S1212 (ECCA).    -   S1208: The base station may perform the signal transmitting        process. When the signal transmission is not performed, the        process proceeds to S1202 (ICCA) and when the signal        transmission is performed, the process proceeds to S1210. Even        in the case where a back-off counter N reaches 0 in S1218 and        S1208 is performed, when the signal transmission is not        performed, the process proceeds to S1202 (ICCA) and when the        signal transmission is performed, the process proceeds to S1210.    -   S1210: When additional signal transmission is not required, the        process proceeds to S1202 (ICCA) and when the additional signal        transmission is required, the process proceeds to S1212 (ECCA).

Extended CCA

-   -   S1212: The base station generates the random number N in the CW.        N is used as a counter during the back-off process and generated        from [0, q−1]. The CW may be constituted by q ECCA slots and an        ECCA slot size may be 9 s or 10 s. The CW size (CWS) may be        defined as q and be variable in S1214. Thereafter, the base        station proceeds to S1216.    -   S1214: The base station may update the CWS. The CWS q may be        updated to a value between X and Y. The X and Y values are        configurable parameters. CWS update/adjustment may be performed        whenever N is generated (dynamic back-off) and semi-statically        performed at a predetermined time interval (semi-static        back-off). The CWS may be updated/adjusted based on exponential        back-off or binary back-off. That is, the CWS may be        updated/adjusted in the form of the square of 2 or the multiple        of 2. In association with PDSCH transmission, the CWS may be        updated/adjusted based on feed-back/report (e.g., HARQ ACK/NACK)        of the user equipment or updated/adjusted based on base station        sensing.    -   S1216: The base station verifies whether the channel is idle for        an ECCA defer period (DeCCA). The ECCA defer period is        configurable. As an implementation example, the ECCA defer        period may be constituted by an interval of 16 μs and n        consecutive CCA slots. Herein, n may be a positive integer and        one CCA slot interval may be 9 s. The number of CCA slots may be        configured differently according to the QoS class. The ECCA        defer period may be set to the appropriate value by considering        the defer period (e.g., DIFS or AIFS) of Wi-Fi. For example, the        ECCA defer period may be 34 us. When the channel is idle for the        ECCA defer period, the base station proceeds to S1218. When it        is determined that the channel is busy during the ECCA defer        period, the base station repeats S1216.    -   S1218: The base station verifies whether N is 0. When N is 0,        the base station may perform the signal transmitting process        (S1208). In this case, (N=0), the base station may not        immediately perform transmission and performs CCA check for at        least one slot to continue the ECCA process. When N is not 0        (that is, N>0), the process proceeds to S1220.    -   S1220: The base station senses the channel during one ECCA slot        interval (T). The ECCA slot size may be 9 s or 10 s and an        actual sensing time may be at least 4 s.    -   S1222: When it is determined that the channel is idle, the        process proceeds to S1224. When it is determined that the        channel is busy, the process returns to S1216. That is, one ECCA        defer period is applied again after the channel is idle and N is        not counted during the ECCA defer period.    -   S1224: N is decreased by 1 (ECCA countdown).

FIG. 13 is substantially the same as/similar to the transmitting processof FIG. 12 and is different from FIG. 12 according to an implementationscheme. Therefore, detailed matters may be described with reference tocontents of FIG. 12.

-   -   S1302: The base station verifies whether the signal transmission        is required. When the signal transmission is not required, S1302        is repeated and when the signal transmission is required, the        process proceeds to S1304.    -   S1304: The base station verifies whether the slot is idle. When        the slot is idle, the process proceeds to S1306 and when the        slot is busy, the process proceeds to S1312 (ECCA). The slot may        correspond to the CCA slot in FIG. 12.    -   S1306: The base station verifies whether the channel is idle for        a defer period (D). D may correspond to the ICCA defer period in        FIG. 12. When the channel is idle for the defer period, the base        station may perform the signal transmitting process (S1308).        When it is determined that the channel is busy during the defer        period, the process proceeds to S1304.    -   S1308: The base station may perform the signal transmitting        process if necessary.    -   S1310: When the signal transmission is not performed, the        process proceeds to S1302 (ICCA) and when the signal        transmission is performed, the process proceeds to S1312 (ECCA).        Even in the case where the back-off counter N reaches 0 in S1318        and S1308 is performed, when the signal transmission is not        performed, the process proceeds to S1302 (ICCA) and when the        signal transmission is performed, the process proceeds to S1312        (ECCA).

Extended CCA

-   -   S1312: The base station generates the random number N in the CW.        N is used as the counter during the back-off process and        generated from [0, q−1]. The CW size (CWS) may be defined as q        and be variable in S1314. Thereafter, the base station proceeds        to S1316.    -   S1314: The base station may update the CWS. The CWS q may be        updated to the value between X and Y. The X and Y values are        configurable parameters. CWS update/adjustment may be performed        whenever N is generated (dynamic back-off) and semi-statically        performed at a predetermined time interval (semi-static        back-off). The CWS may be updated/adjusted based on exponential        back-off or binary back-off. That is, the CWS may be        updated/adjusted in the form of the square of 2 or the multiple        of 2. In association with PDSCH transmission, the CWS may be        updated/adjusted based on feed-back/report (e.g., HARQ ACK/NACK)        of the user equipment or updated/adjusted based on base station        sensing.    -   S1316: The base station verifies whether the channel is idle for        the defer period (D). D may correspond to the ECCA defer period        in FIG. 12. D in S1306 and D in S1316 may be the same as each        other. When the channel is idle for the defer period, the base        station proceeds to S1318. When it is determined that the        channel is busy during the defer period, the base station        repeats S1316.    -   S1318: The base station verifies whether N is 0. When N is 0,        the base station may perform the signal transmitting process        (S1308). In this case, (N=0), the base station may not        immediately perform transmission and performs CCA check during        at least one slot to continue the ECCA process. When N is not 0        (that is, N>0), the process proceeds to S1320.    -   S1320: The base station selects one of an operation of        decreasing N by 1 (ECCA count-down) and an operation of not        decreasing N (self-defer). The self-defer operation may be        performed according to implementation/selection of the base        station and the base station does not perform sensing for energy        detection and not perform even ECCA countdown in the self-defer.    -   S1322: The base station may select one of the operations not        performing sensing for energy detection and the energy detecting        operation. When the sensing for the energy detection is not        performed, the process proceeds to S1324. When the energy        detecting operation is performed, if an energy level is equal to        or lower than an energy detection threshold (that is, idle), the        process proceeds to S1324. If the energy level is higher than        the energy detection threshold (that is, busy), the process        returns to S1316. That is, one defer period is applied again        after the channel is idle and N is not counted during the defer        period.    -   S1324: The process proceeds to S1318.

LBT Scheme for Uplink Transmission

As a method for performing LBT used by terminal(s) in a transmission ofuplink traffic corresponding to an uplink grant, an LBT scheme performedwhen an uplink grant is transmitted may be performed or a singleinterval LBT (hereinafter, referred to as type 2 channel access) such as16 us, 25 us, 34 us or 43 us may be performed when transmitting uplinktraffic within a maximum channel occupancy time (MCOT) secured when theuplink grant is transmitted, thereby enabling fast channel access foruplink data transmission.

Alternatively, as a method for performing LBT used by terminal(s) in atransmission of uplink traffic corresponding to an uplink grant, an LBTscheme performed when an uplink grant is transmitted may be performed ora cat-4 LBT (hereinafter, referred to as type 1 channel access) may beperformed when transmitting uplink traffic outside the MCOT secured whenthe uplink grant is transmitted.

Alternatively, the base station may signal to the terminal whether toperform type 2 channel access enabling a fast channel access, or toperform type 1 channel access in which a random backoff is performed, asan LBT for the uplink traffic. For example, the base station may informthe terminal of either type 1 channel access or type 2 channel accessthrough the uplink grant. In this case, the type 1 channel accessdenotes Cat-4 LBT and type 2 channel access denotes Cat-2 LBT or 25 usLBT.

CWS Adjustment for DL Transmission

FIG. 14 illustrates an example in which a base station performs DLtransmission in an unlicensed band. The base station may aggregate cells(for convenience, LTE-L cell) of one or more licensed bands and cells(for convenience, LTE-U cell, or LAA cell) of one or more unlicensedbands. In FIG. 14, a case in which one LTE-L cell and one LTE-U cell areaggregated for communication with the user equipment is assumed. TheLTE-L cell may be the PCell and the LTE-U cell may be the SCell. In theLTE-L cell, the base station may exclusively use the frequency resourceand perform an operation depending on LTE in the related art. Therefore,all of the radio frames may be constituted by regular subframes (rSF)having a length of 1 ms (see FIG. 2) and the DL transmission (e.g.,PDCCH and PDSCH) may be performed every subframe (see FIG. 1).Meanwhile, in the LTE-U cell, the DL transmission is performed based onthe LBT for coexistence with the conventional device (e.g., Wi-Fidevice). Further, a specific frequency band needs to be allocated orreserved for a specific time in order to effectively implement the LTE-Utechnology/service. Therefore, in the LTE-U cell, the DL transmissionmay be performed through a set of one or more consecutive subframes (DLtransmission burst) after the LBT. The DL transmission burst may startas the regular subframe (rSF) or a partial subframe (pSF) according toan LBT situation. pSF may be a part of the subframe and may include asecond slot of the subframe. Further, the DL transmission burst may endas rSF or pSF.

Hereinafter, a method for adaptively adjusting the CWS in channel accessin the unlicensed band will be described. The CWS may be adjusted basedon user equipment (UE) feed-back and the UE feedback used for the CWSadjustment may include an HARQ-ACK response and a CQI/PMI/RI. Morespecifically, a method for adaptively controlling the CWS based on theHARQ-ACK response will be described. The HARQ-ACK response includes ACK,NACK, and DTX.

For reference, as described with reference to FIG. 11, even in Wi-Fi,the CWS is adjusted based on the ACK. When the ACK is fed back, the CWSis reset to the minimum value (CWmin) and when the ACK is not fed back,the CWS increases. However, since the Wi-Fi is a peer-to-peer (1:1)system, while a cellular system (e.g., LTE) is a multi-access system, itis inefficient to apply a Wi-Fi method as it is and a CWS adjustingmethod considering multiple-access is required.

First, terms are defined as below.

-   -   Set of HARQ-ACK feedback values (HARQ-ACK feedback set): It        means HARQ-ACK feedback value(s) used for updating/adjusting the        CWS. The HARQ-ACK feedback set corresponds to HARQ-ACK feedback        value(s) that is decoded and usable at a time when the CWS is        decided. The HARQ-ACK feedback set includes HARQ-ACK feedback        value(s) for one or more DL (channel) transmission (e.g., PDSCH)        on the unlicensed band (e.g., LTE-U cell). The HARQ-ACK feedback        set may include HARQ-ACK feedback value(s) for the DL (channel)        transmission (e.g., PDSCH), for example, a plurality of HARQ-ACK        feedback values fed back from a plurality of user equipments.        The HARQ-ACK feedback value may represent receiving response        information for the transport block or PDSCH, and represent ACK,        NACK, DTX, and NACK/DTX. According to a context, the HARQ-ACK        feedback value may be used mixedly with the HARQ-ACK        value/bit/response/information, and the like.    -   Reference window: It means a time interval at which the DL        transmission (e.g., PDSCH) corresponding to the HARQ/ACK        feedback set is performed in the unlicensed band (e.g., LTE-U        cell). The reference window may be defined by the unit of SF.        The reference window will be described below in more detail.

In the LTE, according to the HARQ-ACK feedback scheme or a PUCCH format,an HARQ-ACK value may represent only ACK and NACK or further representDTX. For example, when PUCCH format 3 is configured as the HARQ-ACKfeedback method, the HARQ-ACK value may represent only ACK and NACK. Onthe contrary, when a channel selection scheme using PUCCH format 1b isconfigured as the HARQ-ACK feedback method, the HARQ-ACK value mayrepresent ACK, NACK, DTX, and NACK/DTX.

Therefore, a case in which only ACK and e NACK are considered as theHARQ-ACK response, and a case in which the DTX is further considered asthe HARQ-ACK response are separately described. Basic matters are commonto each other.

Case 1: The Case of Considering Only ACK and NACK as a HARQ-ACK Response

The following methods may be considered as a method of adjusting the CWSbased on the HARQ-ACK feedback set. Options 1 to 3 and Alts 1 to 3 maybe combined.

-   -   Option 1: If HARQ-ACK feedback values for the reference window        all are determined as the NACK, the CWS is increased, and if not        (that is, if at least one ACK is present), the CWS may be reset        to a minimum value.    -   Option 2: If at least one of the HARQ-ACK feedback values for        the reference window is determined as the NACK, the CWS is        increased, and if not (that is, if all of the values are the        ACKs), the CWS may be reset to a minimum value.    -   Option 3: If among the HARQ-ACK feedback values for the        reference window, the NACK is determined as at least Z %        (0<Z<100), the CWS is increased, and if not, the CWS may be        reset to a minimum value. As an example, Z may be 50 or 80. That        is, if the ratio (hereinafter, referred to as Y %) of the NACK        in the HARQ-ACK feedback is equal to or more than a reference        value, the CWS is increased, and when the ratio of NACK is less        than the reference value, the CWS may be reset to the minimum        value. The reference value may be 0<reference value <1, or        0%<reference value <100% according to a unit. Equally, if among        the HARQ-ACK feedback values for the reference window, the ACK        is determined as a value less than P % (X=100−Z), the CWS is        increased, and if not, the CWS may be reset to a minimum value.        As an example, P may be 20 or 50.

When the CWS is increased, the CWS may be increased two times, increasedexponentially between a minimum value CW_min and a maximum value CW_max,or increased to the maximum value.

Additionally, when at least one of the following conditions issatisfied, the CWS may be reset to CW_min.

-   -   Alt 1: A case where the maximum CWS, CW_max is used for K        continuous ECCAs. Herein, K is fixed to one of 1, 2, and 3, or        may be selected within {1, . . . , 8} by the base station.    -   Alt 2: A case where there is no DL transmission by the base        station for at least T period. T is a pre-determined value or a        configurable value.    -   Alt 3: A case where the maximum HARQ retransmission is used in K        continuous ECCAs. Herein, K is fixed to one of 1, 2, and 3, or        may be selected within {1, . . . , 8} by the base station.

The reference window may be (1) a single subframe, (2) multi (forexample, two) subframes, or (3) all subframes where the HARQ-ACKfeedback is usable, in the last DL transmission burst (that is, thelatest DL transmission burst on the unlicensed band).

Herein, the (1) single subframe may be the first or last subframe of thelast DL transmission burst. The single subframe may be a regularsubframe rSF or a partial subframe pSF. However, in the partialsubframe, the number of user equipments which may be served by the basestation is limited. Accordingly, when the first or last subframe of thelast DL transmission burst is the partial subframe, the base station mayefficiently adjust the CWS according to channel collision orinterference by defining a HARQ-ACK feedback set based on the HARQ-ACKfeedback value of the user equipment(s) corresponding to the regularsubframe. For example, when the first or last subframe of the last DLtransmission burst is the partial subframe, the reference window may bethe multiple subframes.

Herein, the (2) multi subframes may be a first multiple subframe or thelast multiple subframe in the last DL transmission burst. For example,when the number of multiple subframes is two, the multiple subframes maybe first two subframes of the last DL transmission burst, that is, (1stsubframe) the partial subframe or the regular subframe and (2ndsubframe) the regular subframe. Further, the multiple subframes may bethe last two subframes, that is, (1st subframe) the regular subframe and(2nd subframe) the partial subframe or the regular subframe.

Case 2-1: The Case of Additionally Considering DTX as a HARQ-ACKResponse

Hereinafter, a method of adjusting the CWS by considering ACK, NACK, andDTX, as the HARQ-ACK response transmitted from the user equipment, willbe described. In self-carrier scheduling, that is, in the case where theDL transmission (for example, the PDSCH) for the carrier in theunlicensed band is performed through a control channel (for example,(E)PDCCH) transmitted on the same unlicensed band carrier, the HARQfeedback which may be transmitted by the user equipment with respect tothe DL transmission of the unlicensed band may include ACK, NACK, DTXand NACK/DTX. Herein, since the DTX corresponds to a case where the DLtransmission is unsuccessful by a hidden node and the like in theunlicensed band carrier, the DTX may be used for CWS adjustment togetherwith the NACK. Further, the DTX is one of methods in which the userequipment notifies a case where the user equipment may not decode thecorresponding control channel to the base station even though the basestation transmits the control channel (for example, the (E)PDCCH)including scheduling information to the user equipment. The DTX may bedetermined only by the HARQ-ACK feedback value or determined byconsidering the HARQ-ACK feedback value and an actual schedulingsituation. For convenience, a self-carrier scheduling operation isassumed.

The following methods may be considered as a method of adjusting the CWSbased on the HARQ-ACK feedback set. Methods A-1 to A-4 and methods B-1to B-3 may be combined.

-   -   Method A-1: In the case where all of the HARQ-ACK feedback        values for the reference window are NACK, all of the HARQ-ACK        feedback values are determined as DTX, or all of the HARQ-ACK        feedback values are NACK/DTX, the CWS is increased, and if not        (that is, if at least one ACK is present), the CWS may be reset        to a minimum value.    -   Method A-2: If at least one of the HARQ-ACK feedback values for        the reference window is determined as the NACK, the DTX or the        NACK/DTX, the CWS is increased, and if not (that is, if all of        the values are the ACKs), the CWS may be reset to a minimum        value.    -   Method A-3: If among the HARQ-ACK feedback values for the        reference window, NACK or DTX is determined as at least Z %        (0<Z<100), the CWS is increased, and if not, the CWS may be        reset to a minimum value. As an example, Z may be 50 or 80.        Herein, the NACK or the DTX of at least Z % means that either        the NACK or the DTX is added, i.e., a sum of NACK, DTX and        NACK/DTX, to become at least Z %. That is, NACK/DTX and DTX may        be treated equally with NACK. Accordingly, if a ratio        (hereinafter, referred to as Y %) of NACK or DTX in the HARQ-ACK        feedback is equal to or more than a reference value, the CWS is        increased, and when the ratio of NACK or DTX is less than the        reference value, the CWS may be reset to the minimum value. The        reference value may be 0<reference value <1, or 0%<reference        value <100% according to a unit. Equally, if among the HARQ-ACK        feedback values for the reference window, the ACK is determined        as a value less than P % (X=100-Z), the CWS is increased, and if        not, the CWS may be reset to a minimum value. As an example, P        may be 20 or 50.    -   Method A-4: In the case where all of the HARQ-ACK feedback        values for the reference window are determined as the DTX, the        base station increases the CWS by considering that all of the        control channels PDCCH/EPDCCH are not received by the user        equipment or the decoding of both the PDCCH and the EPDCCH is        unsuccessful by interference of other nodes, and if not (that        is, in the case where all of the HARQ-ACK feedback values are        not determined as the DTX), the CWS may be adjusted according to        the methods A-1 to A-3.

When the CWS is increased, the CWS may be increased two times, increasedexponentially between a minimum value CW_min and a maximum value CW_max,or increased to the maximum value.

Additionally, when at least one of the following conditions issatisfied, the CWS may be reset to CW_min.

-   -   Method B-1: A case where the maximum CWS CW_max is used for K        continuous ECCAs. Herein, K is fixed to one of 1, 2, and 3, or        may be selected within {1, . . . , 8} by the base station.    -   Method B-2: A case where there is no DL transmission by the base        station for at least T period. T is a pre-determined value or a        configurable value.    -   Method B-3: A case where the maximum HARQ retransmission is used        within K continuous ECCAs. Herein, K is fixed to one of 1, 2,        and 3, or may be selected within {1, . . . , 8} by the base        station.

The reference window may be (1) a single subframe, (2) multi (forexample, two) subframes, or (3) all subframes where the HARQ-ACKfeedback is usable in the last DL transmission burst (that is, thelatest DL transmission burst on the unlicensed band). The detailedcontents may refer to the contents described in Case 1.

Case 2-2: The Case of Additionally Considering DTX as a HARQ-ACKResponse

Hereinafter, another example of the method of adjusting the CWS byconsidering ACK, NACK, and DTX, as the HARQ-ACK response transmittedfrom the user equipment, will be described. In self-carrier scheduling,that is, in the case where the DL transmission (for example, the PDSCH)for the carrier in the unlicensed band is performed through a controlchannel (for example, (E)PDCCH) transmitted on the same unlicensed bandcarrier, the HARQ feedback which may be transmitted by the userequipment with respect to the DL transmission in the unlicensed band mayinclude ACK, NACK, DTX and NACK/DTX. Herein, since the DTX correspondsto a case where the DL transmission is unsuccessful by a hidden node andthe like in the unlicensed band carrier, the DTX may be used for CWSadjustment together with the NACK. Further, the DTX disclosed herein isone of methods in which the user equipment notifies a case where theuser equipment does not decode the corresponding control channel to thebase station even though the base station transmits the control channel(for example, the (E)PDCCH) including scheduling information to the userequipment. The DTX may be determined only by the HARQ-ACK feedback valueor determined by considering the HARQ-ACK feedback value and an actualscheduling situation. For convenience, a self-carrier schedulingoperation is assumed.

The following methods may be considered as a method of adjusting the CWSbased on the HARQ-ACK feedback set. Methods C-1 and C-2 and methods D-1to D-3 may be combined.

-   -   Method C-1: In the case where there is the DTX in the HARQ-ACK        feedback values for the reference window, a weight value may be        applied to the DTX when calculating Y % based on the NACK or the        DTX, as the HARQ-ACK feedback, according to the method A-3. In        the case where the base station may distinguish the NACK and the        DTX and in the case where the user equipment feedbacks the DTX        even though the base station transmits a PDSCH related with a        control channel PDCCH/EPDCCH, the base station may know that the        corresponding user equipment does not receive the control        channel PDCCH/EPDCCH. In this case, the base station may        recognize that there is a possibility that an interference or        hidden node and the like occurs in the corresponding channel.        Accordingly, when receiving the DTX from the user equipment, the        base station may calculate Y % by applying the weight value to        the DTX in order to more positively solve the problem generated        by the interference or hidden node on the channel. Further, when        the NACK/DTX is included in the HARQ-ACK feedback values within        the reference window, the base station may regard the NACK/DTX        as the NACK. Unlike this, when the user equipment feedbacks the        NACK/DTX to the base station, it is meaningful that the user        equipment notifies to the base station that the HARQ-ACK        feedback values may be the DTX. Accordingly, when the NACK/DTX        is fed back from the user equipment, the base station may        calculate Y % by applying the weight value to the NACK/DTX in        the HARQ-ACK feedback set. Values considered as the HARQ-ACK        feedback may be ACK, NACK, NACK/DTX, and DTX. As described        herein, Y % for adjusting the CWS may be calculated by        considering different weight values for the NACK, the NACK/DTX,        and the DTX except for the ACK.

Equation 1 represents one example of the method C-1. The method may besimilarly expressed by another equation and is not limited by thefollowing Equation.

Y %={W_A*Pr(A)+W_B*Pr(B)+W_C*Pr(C)}*100,  [Equation 1]

Herein, Pr(A) represents a probability of the NACK in the referencewindow, that is, Pr(A)=the number of NACKs/the total number of usableHARQ-ACK feedbacks in the reference window. Herein, Pr(B) represents aprobability of the NACK/DTX in the reference window, that is, Pr(B)=thenumber of NACK/DTXs/the total number of usable HARQ-ACK feedbacks in thereference window. Herein, Pr(C) represents a probability of the NACK/DTXin the reference window, that is, Pr(C)=the number of DTXs/the totalnumber of usable HARQ-ACK feedbacks in the reference window. W_A means aweight value for the NACK, W_B means a weight value for the NACK/DTX,and W_C means a weight value for the DTX.

First, W_A=W_B=W_C is a case where the NACK, the NACK/DTX, and the DTXare calculated with the same weight value in the HARQ-ACK feedback setwhen calculating Y %. W_A<W_B=W_C is a case where the NACK/DTX and theDTX are calculated with a larger weight value than that of the NACK andthe NACK/DTX and the DTX are calculated with the same weight value inthe HARQ-ACK feedback set when calculating Y %. W_A=W_B<W_C is a casewhere the NACK and the NACK/DTX are calculated with the same weightvalue and the DTX is calculated with a larger weight value in theHARQ-ACK feedback set when calculating Y %. W_A<W_B=W_C is a case wherethe NACK/DTX is calculated with a larger weight value than the NACK andthe DTX is calculated with a larger weight value than the NACK/DTX inthe HARQ-ACK feedback set when calculating Y %.

-   -   When the calculated Y % is at least Z %, the CWS is increased,        and if not, the CWS may be reset to a minimum value. Herein, Z %        is a reference value which may be set in the base station (for        example, 0<Z<100). For example, Z may be 50 or 80.    -   Method C-2: When there is at least one DTX feedback for the        reference window, the CWS may be increased. The method is a        method of overriding to the option-3 or the method A-3. If not        (that is, No DTX), the CWS may be adjusted according to the        option-3 or the method A-3. Since the DTX represents that the        user equipment does not receive the control channel PDCCH/EPDCCH        on the unlicensed band due to the interference or hidden node in        the same channel, the base station may increase the CWS as the        method for solving the problem.

When the CWS is increased, the CWS may be increased two times, increasedexponentially between a minimum value CW_min and a maximum value CW_max,or increased to the maximum value.

Additionally, when at least one of the following conditions issatisfied, the CWS may be reset to CW_min.

-   -   Method D-1: A case where the maximum CWS CW_max is used for K        continuous ECCAs. Herein, K is fixed to one of 1, 2, and 3, or        may be selected within {1, . . . , 8} by the base station.    -   Method D-2: A case where there is no DL transmission by the base        station for at least T period. T is a pre-determined value or a        settable value.    -   Method D-3: A case where the maximum HARQ retransmission is used        in K continuous ECCAs. Herein, K is fixed to one of 1, 2, and 3,        or may be selected within {1, . . . , 8} by the base station.

The reference window may be (1) a single subframe, (2) multi (forexample, two) subframes, or (3) all subframes where the HARQ-ACKfeedback is usable in the last DL transmission burst (that is, thelatest DL transmission burst on the unlicensed band). The detailedcontents may refer to the contents described in Case 1.

Cases 2-1 and 2-2 may be differently applied as described belowaccording to whether the scheduling cell is a LTE-L cell or a LTE-U cellin the cross-carrier scheduling.

-   -   In the case where the DL transmission transmitted in the        unlicensed carrier is cross-carrier scheduled from a different        unlicensed band (that is, an unlicensed carrier, an unlicensed        band cell, and an LTE-U cell), the CWS may be adjusted by using        the same method as the self-carrier scheduling. The reason is        that since the control channels (e.g., the PDCCH/EPDDCH) are        transmitted in the unlicensed carrier, the determination of the        base station based on the HARQ-ACK response(s) (ACK, NACK, DTX        and NACK/DTX) may be equally performed with the case of the        self-carrier scheduling.    -   In the case where the DL transmission transmitted in the        unlicensed carrier is cross-carrier scheduled from a licensed        band (that is, a licensed carrier, a licensed band cell, and an        LTE-L cell), the PDCCH/EPDCCH which are the control channels        scheduling the DL transmission is transmitted in the licensed        band. In this case, since the DTX feedback is used to determine        a decoding situation of the user equipment for the control        channel transmitted on the licensed band, it doesn't help        adaptively adjusting the CWS for channel access in the        unlicensed band. Accordingly, in the cross-carrier scheduling        from the licensed band, the method of adjusting the CWS        considering the DTX is set not to be used, and the CWS may be        adjusted by considering only the ACK and the NACK as the        HARQ-ACK response(s) for the DL transmission (for example,        PDSCH) on the unlicensed band. Alternatively, the CWS may be        adjusted by considering only the ACK, the NACK and the NACK/DTX        as the HARQ-ACK response(s) for the DL transmission (for        example, PDSCH) on the unlicensed band. For example, the DTX as        the HARQ-ARQ response due to the cross-carrier scheduling from        the licensed band may be excluded in the process of applying the        cases 1, 2-1, and 2-2. In detail, in the option 3 and the method        A-3, the DTX as the HARQ-ARQ response due to the cross-carrier        scheduling from the licensed band may be excluded when        calculating Z %. That is, in the HARQ-ACK feedback set, only the        ACK and the NACK are selected to calculate Z % or only the ACK,        the NACK and the NACK/DTX are selected to calculate Z %. In        addition, the following two methods are available for the base        station to calculate Z % excluding DTX in Option 3 and Method        A-3.    -   First, DTX indicating failure in receiving control channel at        the user equipment for control channel transmission on the        licensed cell is not included in the entire HARQ-ACK value(s)        and is not included in the ratio of NACK, when determining Z %.    -   Second, DTX indicating failure in receiving control channel at        the user equipment for control channel transmission on the        licensed cell is included in the entire HARQ-ACK value(s) but is        not included in the ratio of NACK, when determining Z %.    -   As described above, if the DL transmission transmitted on the        unlicensed carrier is cross-carrier scheduled from a licensed        band (i.e., a licensed carrier, a licensed band cell, and an        LTE-L cell), the DTX as a HARQ-ACK response by cross-carrier        scheduling from the licensed band may be excluded from the        procedures applying Cases 1, 2-1, and 2-2. Specifically, DTX as        a HARQ-ACK response by cross-carrier scheduling from the        licensed band may be excluded when calculating Z % in option 3        and method A-3. In addition, the following two methods are        available for the base station to calculate Z % excluding DTX in        Option 3 and Method A-3.    -   First, DTX indicating failure in receiving control channel at        the user equipment for control channel transmission on the        licensed cell is not included in the entire HARQ-ACK value(s)        and is not included in the ratio of NACK, when determining Z %.    -   Second, DTX indicating failure in receiving control channel at        the user equipment for control channel transmission on the        licensed cell is included in the entire HARQ-ACK value(s) but is        not included in the ratio of NACK.

However, when HARQ-ACK feedback is performed using a channel selectionscheme based on the PUCCH format 1b (i.e., PUCCH format 1b with channelselection), even if the user equipment performs no transmission, thebase station may determine the HARQ-ACK response according to the notransmission. Specifically, the base station may determine the HARQ-ACKresponse corresponding to the no transmission based on the HARQ-ACKresponse values of Tables 3 to 5 defined for A=2 to 4. For example, whenA=2, if the user equipment performs no transmission, the base stationmay determine that the HARQ-ACK response corresponding to the notransmission is [HARQ-ACK (0), HARQ-ACK (1)]=[DTX, NACK/DTX] based onTable 3.

-   -   If the DL transmission transmitted on an unlicensed carrier is        cross-carrier scheduled from a licensed band (i.e., a licensed        carrier, a licensed band cell, and an LTE-L cell) and the user        equipment is configured to transmit a HARQ-ACK response using a        channel selection scheme based on the PUCCH format 1b, in the        cases other than (i) the case of no transmission from the user        equipment and (ii) the case where the base station fails to        detect the HARQ-ACK response, the NACK/DTX state and the any        state as the HARQ-ACK response may be regarded as a NACK when        calculating Z % for adjusting the CWS. That is, if there is an        HARQ-ACK response explicitly, the NACK/DTX state and the any        state may be regarded as a NACK when calculating Z %. On the        other hand, in the case where (i) there is no transmission from        the user equipment or (ii) the base station fails to detect the        HARQ-ACK response, the HARQ-ACK response(s) determined by the        base station as a DTX may be excluded when calculating Z %. In        this case, as a method for configuring a DTX to be excluded when        calculating Z %, the following two methods are possible.    -   First, since the corresponding DTX may not reflect the channel        state of the unlicensed cell, the DTX is not included in the        entire HARQ-ACK value(s) and is not included in the ratio of        NACK, when determining Z %.    -   Second, the corresponding DTX is included in the entire HARQ-ACK        value(s) but is not included in the ratio of NACK.

Unlike this, in the case where there is no transmission from the userequipment or (ii) when the base station fails to detect the HARQresponse, the HARQ-ACK response(s) determined by the base station as aNACK/DTX may be considered as a NACK when calculating Z %. This may be amethod for allowing a CWS adjustment to be performed by the base stationby assuming the possibility of a NACK for DL transmission on theunlicensed carrier. Unlike this, in the case where (i) the userequipment indicates a NACK/DTX with the no transmission or (ii) the basestation does not detect the HARQ-ACK response, the HARQ-ACK response(s)determined by the base station as a NACK/DTX are regarded as a DTX, nota NACK, when calculating Z % in order not to include the NACK/DTX in Z%. Accordingly, the NACK/DTX state may be ignored. Specifically, sinceit is impossible to determine whether (i) and (ii) are due to an errorin the PDCCH/EPDCCH transmission in the licensed carrier or resultedfrom the case that a PUCCH detection is not performed by the basestation because the channel state of the channel through which a PUCCHon a licensed carrier is transmitted is not in a good condition while aNACK for a PDSCH transmitted through an unlicensed carrier istransmitted by the user equipment transmits through the PUCCH on thelicensed carrier. Accordingly, the corresponding NACK/DTX state may beregarded as a DTX when calculating Z %, so that it may not be regard asthe NACK when calculating Z % of NACK. That is, the NACK/DTX state maybe ignored so as not to be included in Z %. Here, the following twomethods are available for the base station to determine Z % ignoring theNACK/DTX, without including the NACK/DTX.

-   -   First, since the DTX, indicating failure in receiving control        channel at the user equipment for control channel transmission        on the licensed cell, may not reflect the channel state of the        unlicensed cell, it is possible to configure the NACK/DTX not to        be included in the entire HARQ-ACK value(s), and not to be        included in the ratio of NACK, when determining Z %.    -   Second, since the DTX, indicating failure in receiving control        channel at the user equipment for control channel transmission        on the licensed cell, may not reflect the channel status of the        unlicensed cell, it is possible to configure the NACK/DTX to be        included in the entire HARQ-ACK value(s), but not to be included        in the ratio of NACK.

Meanwhile, when a part of the HARQ-ACKs is determined to be DTX andanother part of the HARQ-ACKs is determined to be NACK/DTX in theprocess of detecting a HARQ-ACK for the no transmission, the DTX as apart of the HARQ-ACKs may be reflected in calculation of the Z %identically to the NACK/DTX. For example, if the NACK/DTX is regarded asa NACK to be reflected in Z %, the DTX may also be determined as a NACKto be reflected in Z % of the NACK. On the other hand, if the NACK/DTXis not reflected in Z %, the DTX may be regarded as the DTX not to bereflected in Z %. Here, the following two methods are available for amethod for setting the base station not to reflect the DTX whendetermining Z %.

-   -   First, since the DTX, indicating failure in receiving control        channel at the user equipment for control channel transmission        on the licensed cell, does not reflect a channel state of an        unlicensed cell, the DTX is not included in the entire HARQ-ACK        value(s) and is not included in the ratio of NACK, when        determining Z %.    -   Second, the DTX, indicating failure in receiving control channel        at the user equipment for control channel transmission on the        licensed cell, is included in the entire HARQ-ACK value(s) but        is not included in the ratio of NACK.

FIGS. 15 to 17 illustrate a signal transmitting process. FIG. 15illustrates a method for adjusting a CWS according to case 1 and FIGS.16 and 17 illustrate a reference window for generating an HARQ-ACKfeedback set. Cases 2-1 and 2-2 may be similarly performed.

Referring to FIG. 15, the base station may transmit an n-th DLtransmission burst in the unlicensed band (e.g., LTE-U cell) (S1502) andthereafter, transmit an (n+1)-th DL transmission burst based on the ECCAwhen additional DL transmission is required (S1512). In detail, the basestation additionally performs the random back-off in the CW when thechannel in the unlicensed band is idle during the ECCA defer period(S1510). The base station may generate a random number N in the CW(e.g., [0, q−1]) (S1508) and perform the back-off as long as slotscorresponding to the random number N (S1510). Herein, the CWS isadaptively varied based on the HARQ-ACK feedback values from userequipments (S1506). The HARQ-ACK feedback values used for adjusting theCWS include HARQ-ACK feedback values for a most recent DL transmissionburst (n-th DL transmission burst). The HARQ-ACK feedback values usedfor adjusting the CWS include HARQ-ACK feedback values for the DLtransmission on the reference window in the DL transmission burst(S1504).

When case 1 is applied, the CWS may be adjusted as follows based on theHARQ-ACK feedback values. Cases 2-1 and 2-2 may be similarly applied.

-   -   Option 1: When all of the HARQ-ACK feedback values for the        reference window are NACK, the CWS is increased and if not, the        CWS is reset to the minimum value.    -   Option 2: When at least one of the HARQ-ACK feedback values for        the reference window is the NACK, the CWS is increased and if        not, the CWS is reset to the minimum value.    -   Option 3: When the NACK among the HARQ-ACK feedback values for        the reference window is at least Z % (0<Z<100), the CWS is        increased and when the NACK is not at least Z %, the CWS is        reset to the minimum value.

When the CWS is increased, the CWS may be increased twice, exponentiallyincreased between the minimum value (CW_min) and a maximum value(CW_max), or increased to the maximum value.

Referring to FIGS. 16 and 17, the reference window may be constituted bystart subframe(s) (FIG. 16) and last subframe(s) (FIG. 17) of the mostrecent DL transmission burst (n-th DL transmission burst). When thereference window is positioned at the start of the DL transmissionburst, the reference window may be constituted by (i) one regularsubframe and (ii) one partial subframe and one regular subframe.Further, when the reference window is positioned at the end of the DLtransmission burst, the reference window may be constituted by (i) oneregular subframe and (ii) one regular subframe and one sub subframe.

The present method assumes that a HARQ-ACK response transmitted from theuser equipment is transmitted through a PUCCH or a PUSCH on a PCell of alicensed band.

Next, when the user equipment is configured to transmit ACK, NACK,NACK/DTX, and DTX values as a HARQ-ACK response for PDSCH(s) transmittedthrough DL on an unlicensed carrier through UL on the unlicensedcarrier, a method for performing CW size update/adjustment fortransmission in the base station will be described.

A case where the HARQ-ACK for the PDSCH(s) transmitted through the DL onLAA SCell is transmitted only through the UL on the unlicensed carrieror the LAA SCell will be described.

-   -   In a method 100, in a case where HARQ-ACK for PDSCH(s)        transmitted through a DL on an unlicensed carrier or an LAA        SCell is transmitted only through a UL on an unlicensed carrier        or an LAA SCell, if at least one ACK is fed back as the        HARQ-ACK(s) transmitted through the UL on the LAA SCell, the        base station may reset the CW size for DL PDSCH(s) transmissions        on the LAA SCell, and otherwise may increase the CW size (e.g.,        double). That is, when the base station successfully decodes a        PUCCH or a PUSCH including the HARQ-ACK transmitted from the        user equipment on the LAA SCell and detects at least one ACK        from the user equipment for the PDSCH(s) transmitted from the        base station, the base station may reset the CW size. In this        case, the base station determines that the channel for the        medium between the base station and the user equipment is idle        to reset every CWp (e.g., p={1, 2, 3, 4}) that may be        differently set according to a channel access priority class to        CWmin. In addition, when the user equipment transmits feedback        with NACK since the user equipment fails to decode the PDSCH(s)        and the base station detects or determines NACK, NACK/DTX, or        DTX, the base station may double the CW. Alternatively, even in        the case of detecting NACK, NACK/DTX, or DTX at the base        station, which may occur due to the transmission of the PUCCH or        the PUSCH including the HARQ-ACK transmitted from the user        equipment is transmitted on the unlicensed carrier, the base        station may double the CW. In this case, the base station may        determine that the channel for the medium between the base        station and the user equipment is busy and double the CWp (e.g.,        p={1, 2, 3, 4}) that may be differently set according to the        channel access priority class. Further, if the LBT using the        CW_max value is repeatedly set to K times (e.g., K={1, . . . ,        8}) after doubling the CW size, CWp may be set to the CW_min        value. The value K may be designated to one value of {1, . . . ,        8} by the base station.

When the number of unlicensed carriers increases, it may be impossibleto transmit the HARQ-ACK value only through a UL on a specific singleunlicensed carrier. In this case, the HARQ-ACK transmission may beperformed through the UL in units of a group in which transmission of anHARQ-ACK response is possible and set by the RRC. Meanwhile, when thereis not much DL PDSCH transmission on the unlicensed carrier, it ispossible to transmit the HARQ-ACK response only through a UL on a singleLAA SCell. When the HARQ-ACK transmission is performed through the UL ofa group unit, an unlicensed carrier (e.g., an LAA SCell index) on whichthe transmission of the HARQ-ACK depending on channel availability basedon a channel access within a group may be configured to dynamically varyin units of a subframe, or may be configured to a single semi-staticunlicensed carrier (e.g., LAA SCell). The base station receiving thefeedback on the HARQ-ACK(s) based on the group may update/adjust a CWpand a group_index by managing the CWp and the group_index for the DLPDSCH to be transmitted to the user equipment based on the group. Basedon the feedback of the HARQ-ACK of the DL PDSCH(s) on the LAA SCELL(s)configured as the group, CW size may be reset or doubled.

A case where HARQ-ACK feedbacks for PDSCH(s) transmitted on anunlicensed carrier or an LAA SCell are divided into HARQ-ACK feedbackstransmitted through a PUCCH or a PUSCH on licensed carriers and HARQ-ACKfeedbacks transmitted through a PUCCH or a PUSCH on unlicensed carrierswill be described.

-   -   In a method 110, the HARQ-ACK feedbacks for PDSCH(s) transmitted        on an unlicensed carrier or an LAA SCell are divided into the        HARQ-ACK feedbacks transmitted through the PUCCH or the PUSCH on        the licensed carrier and the HARQ-ACK feedbacks transmitted        through the PUCCH or the PUSCH on the unlicensed carrier. In        this case, based on the Z % of NACK (e.g., 80 or 50, which may        be a natural number value set by the base station), if the        feedback determined as NACK is Z % or more, the CW size        update/adjustment according to the HARQ-ACK feedback transmitted        through the UL on the licensed carrier doubles the CW, otherwise        the CW size update/adjustment resets the CW size. When a        HARQ-ACK feedback is transmitted on the licensed carrier among        the HARQ-ACK feedbacks for PDSCHs transmitted on the LAA cell, a        CW size for an LAA SCell transmitting the PDSCH corresponding to        the HARQ-ACK transmitted on the licensed carrier may be        updated/adjusted using Methods A-1, A-2, A-3, A-4, B-1, B-2,        B-3, and a combination thereof. If the LBT using the CW_max        value is repeatedly set to K times (e.g., K={1, . . . , 8})        after doubling the CW size, CWp may be set to the CW_min value.        The value K may be designated to one value of {1, . . . , 8} by        the base station.

In case of the CW size update/adjustment according to the HARQ-ACKfeedback transmitted through the UL on the unlicensed carrier, the groupof the HARQ-ACK corresponding to the PDSCH(s) transmitted through the DLon the LAA SCell is transmitted only through the UL on the unlicensedcarrier or the LAA SCell may be limited to the LAA SCell transmittingthe PDSCH corresponding to the HARQ-ACK transmitted on the unlicensedcarrier. Therefore, the same method as in Method 100 can be applied toperform CW size update/adjustment for the PDSCH transmitted on the LAASCell. If the LBT using the CW_max value is repeatedly set to K times(e.g., K={1, . . . , 8}) after doubling the CW size, CWp may be set tothe CW_min value. The value K may be designated to one value of {1, . .. , 8} by the base station.

Unlike the method for updating/adjusting the CW size according towhether the cell transmitting the HARQ-ACK independently is theunlicensed cell (e.g., LAA SCell) or the licensed cell, by referringboth the HARQ-ACK feedback on the licensed carrier and the HARQ-ACKfeedback on the unlicensed carrier, a method for managing the CW sizefor the LBT of the DL PDSCH transmission on the unlicensed carrier orthe LAA SCell may also be considered. When conditions of methods 100 and110 as a hybrid method of the method 100 and the method 110, that is, acase (i.e., Condition-110) where ACK detection as a feedback valuetransmitted through the UL on the unlicensed carrier is performed by thebase station and a case (i.e., Condition-110) where the feedback that isregarded as NACK is not equal to or more than Z %, are both satisfied,CW size may be reset. However, when both conditions are not satisfied,CW size may be doubled. Alternatively, since Condition-100 considers ULtransmission on an unlicensed carrier, it is determined that the channelstate of the unlicensed carrier may be better reflected so that CW sizemay be reset or doubled depending on whether Condition-100 is satisfied.Unlike this, Condition-110, which is designed to better reflect thechannel state of all UEs, is considered to better reflect the channelstate of unlicensed carriers in all UEs, so that a method for resettingor doubling the CW size according to whether Condition-110 is satisfiedmay be considered. If the LBT using the CW_max value is repeatedly setto K times (e.g., K={1, . . . , 8}) after doubling the CW size, CWp maybe set to the CW_min value. The value K may be designated to one valueof {1, . . . , 8} by the base station.

In the LTE system up to the existing Rel-13, if a simultaneoustransmission of PUSCH and PUCCH is set in a user equipment, thesimultaneous transmission of PUSCH and PUCCH may be performed in thesame carrier or in different carriers. However, if the simultaneoustransmission of PUSCH and PUCCH is not configured in the user equipment,in a case where the PUSCH transmission is not scheduled in thecorresponding subframe, transmission of UCI such as HARQ-ACK and CSI isperformed on the PUCCH, and in a case where the PUSCH transmission isscheduled in the corresponding subframe, the transmission of UCI such asthe HARQ-ACK and the CSI to be transmitted through the PUCCH ispiggybacked to the PUSCH. This applies equally to different carrierswhen carrier aggregation is performed.

In this case, in performing carrier aggregation, in cases whereaggregated carriers are composed of different licensed carriers andunlicensed carriers, it is assumed that a group of cells on whichtransmission of a PUCCH is possible is composed of licensed carrier(s)and unlicensed carrier(s). In this case, if simultaneous transmission ofPUSCH and PUCCH is configured in the user equipment, HARQ-ACK and CSI asuser equipment feedback for DL transmissions transmitted on the licensedcarrier(s) may be transmitted through the PUCCH on the licensedcarrier(s), but the HARQ-ACK may not be transmitted through a scheduledPUSCH on the unlicensed carrier(s), and the CSI (e.g., periodic CSI oraperiodic CSI) may be transmitted to the scheduled PUSCH on theunlicensed carrier(s). In addition, if HARQ-ACK and CSI as userequipment feedback for DL transmissions transmitted on unlicensedcarriers are transmitted through the PUCCH on the licensed carrier or ifthe PUSCH on the unlicensed carrier is scheduled, transmission throughthe corresponding PUSCH may be possible.

However, if simultaneous transmission of PUSCH and PUCCH is notconfigured in the user equipment, HARQ-ACK and CSI as a feedback fromthe user equipment for DL transmissions transmitted from licensedcarriers may be transmitted through a PUCCH on the licensed carriers,but the HARQ-ACK may not be transmitted through a scheduled PUSCH on theunlicensed carrier, and CSI (e.g., periodic CSI or aperiodic CSI) may betransmitted through the scheduled PUSCH on an unlicensed carrier.According to the method used in the existing LTE system, if the PUSCH isnot scheduled in the corresponding subframe, HARQ-ACK and CSI as a userequipment feedback for DL transmission on the licensed carrier and onthe unlicensed carrier are transmitted through the PUCCH on the licensedcarrier, and if the PUSCH is scheduled in the corresponding subframe onthe licensed carrier or on the unlicensed carrier, only the scheduledPUSCH is transmitted by piggybacking HARQ-ACK and CSI as the userequipment feedback for DL transmission on the licensed carrier and onthe unlicensed carrier with a scheduled PUSCH on a licensed carrier oron an unlicensed carrier However, since HARQ-ACK as the user equipmentfeedback for DL transmission transmitted on licensed carriers isconfigured not to be transmitted on unlicensed carrier, if the PUSCH isscheduled on the unlicensed carrier, the HARQ-ACK response as the userequipment feedback for the DL transmission transmitted on the licensedcarrier may not be transmitted through the scheduled PUSCH on theunlicensed carrier. Therefore, the following options may be consideredin order to solve the corresponding case.

-   -   Option 1. In a case where the configuration of a carrier        aggregation (CA) is composed of licensed carriers and unlicensed        carriers, as a group of cells on which transmission of a PUCCH        is possible, it is composed of licensed carrier(s) and        unlicensed carrier(s), and if simultaneous transmission of PUSCH        and PUCCH is not configured in the user equipment, in a subframe        where transmission of the PUCCH may be performed, the user        equipment does not expect transmission of the PUSCH to be        scheduled on the unlicensed carrier from the base station, and        the user equipment assumes only the transmission of the PUCCH,        so that HARQ-ACK and CSI as a user equipment feedback for DL        transmission on the licensed carrier and on the unlicensed        carriers are transmitted through the PUCCH on the licensed        carrier.    -   Option 2. In a case where the configuration of the CA is        composed of licensed carriers and unlicensed carriers, as a        group of cells on which transmission of a PUCCH is possible, it        is composed of licensed carrier(s) and unlicensed carrier(s),        and if simultaneous transmission of PUSCH and PUCCH is not        configured in the user equipment, for a subframe where        transmission of the PUCCH may be possible, as a user equipment        feedback for DL transmission on the licensed carrier to be        transmitted by the user equipment, only when the HARQ-ACK        response is a subframe to be transmitted, the user equipment        does not expect the PUSCH transmission to be scheduled on the        unlicensed carrier from the base station. In addition, the user        equipment assumes only the transmission of the PUCCH, so that        HARQ-ACK and CSI as the user equipment feedback for DL        transmission on the licensed carrier and on the unlicensed        carrier are transmitted through the PUCCH on the licensed        carrier. Since only the HARQ-ACK response for the DL        transmission on the licensed carrier may not be transmitted to        the PUSCH on the unlicensed carrier, the CSI may be transmitted        to the PUSCH on the unlicensed carrier. Therefore, only when the        UCI type to be piggybacked is the HARQ-ACK response for the DL        transmission on the licensed carrier, the method may be applied.    -   Option 3. In a case where the CA is composed of licensed        carrier(s) and unlicensed carrier(s), as a group of cells on        which transmission of a PUCCH is possible, and the simultaneous        transmission of PUSCH and PUCCH is not configured in the user        equipment, for a subframe where PUCCH transmission may be        possible, if the PUSCH transmission is scheduled on the        unlicensed carrier from the base station, the user equipment        configures HARQ-ACK and CSI as a user equipment feedback for DL        transmissions on the licensed carrier and on the unlicensed        carrier, to be transmitted through the PUSCH on the unlicensed        carrier, by using the legacy UCI piggyback method.    -   Option 4. In a case where the CA is composed of licensed        carrier(s) and unlicensed carrier(s), as a group of cells on        which transmission of a PUCCH is possible, and the simultaneous        transmission of PUSCH and PUCCH is not configured in the user        equipment, for a subframe where PUCCH transmission may be        possible, if the PUSCH transmission is scheduled on the        unlicensed carrier from the base station, the user equipment        drops the scheduled PUSCH on the unlicensed carrier, and the        user equipment configures HARQ-ACK and CSI as the user equipment        feedback for DL transmissions on the licensed carrier and on the        unlicensed carrier to be transmitted through the PUCCH on the        licensed carrier, by assuming the transmission only through the        PUCCH.    -   Option 5. In a case where the CA is composed of licensed        carrier(s) and unlicensed carrier(s), as a group of cells on        which transmission of a PUCCH is possible, and the simultaneous        transmission of PUSCH and PUCCH is not configured in the user        equipment, for a subframe where PUCCH transmission may be        possible, if a PUSCH transmission is scheduled on the unlicensed        carrier from a base station, the user equipment drops the        scheduled PUSCH as only when the subframe is the HARQ-ACK        response to be transmitted as an user equipment feedback for DL        transmission on the licensed carrier to be transmitted by the        user equipment. In addition, the user equipment configures        HARQ-ACK and CSI as the user equipment feedback for DL        transmissions on the licensed carrier and on the unlicensed        carrier to be transmitted through the PUCCH on the licensed        carrier, by assuming the transmission only through the PUCCH.        Since only the HARQ-ACK response to the DL transmission on the        licensed carrier may not be transmitted through the PUSCH on the        unlicensed carrier, the CSI may be transmitted through the PUSCH        on an unlicensed carrier. Therefore, only when the UCI type to        be piggybacked is the HARQ-ACK response to the DL transmission        on the licensed carrier, it may drop the scheduled PUSCH on the        unlicensed carrier by applying the corresponding method.

<Exclusion Method for Calculating NACK Rate for PUSCH Transmission Dropin Adjusting CWS>

In Options 4 to 5, the base station may schedule the PUSCH, but the userequipment may drop the PUSCH. If a CWS adjustment is used based on thePUSCH reception of the base station at UL LBT, in the case of Options 4to 5, since the base station may recognize the PUSCH drop from the userequipment according to the combination of the configuration information,for the PUSCH drop of the user equipment, during the CWS adjustment, thecorresponding PUSCH drop may not indicate the collision handling orinterference condition on the unlicensed carrier(s). Accordingly, thedropped PUSCH may be configured not to be used for calculating the NACKratio for the CWS adjustment or calculating Z % of the NACK used for DLCWS adjustment.

The representation of the unlicensed carrier(s) in the presentdisclosure may be identical to that of the LAA SCell(s).

CWS Adjustment for UL Transmission

A method for adjusting a CWS for the UL LBT of the user equipment willbe described.

When a base station manages a user equipment-specific CWS of each ofuser equipment(s), or each of the user equipment(s) enables the basestation to recognize the CWS of each user equipment, the base stationmay update/adjust the CWS of each user equipment based on the ULtransmissions transmitted from the user equipment. Meanwhile, in thecase of power limitation of a user equipment, depending on a priority ofchannels of licensed carrier(s) and channels of unlicensed carrier(s), aPUSCH transmission may be dropped on the unlicensed carrier(s). However,since the base station may difficult to recognize the power limitationstate of the user equipment, it is impossible to recognize whether thechannels dropped by the user equipment are transmitted due to the powerlimitation. The base station expects the user equipment to transmit thescheduled channel and expects UL reception at the correspondingreception timing. Accordingly, when the UL transmission is dropped inthe user equipment, the base station may determine a reception responsefor the UL transmission to a NACK and use the NACK as information forupdating the CWS of the use equipment. However, due to the powerlimitation state of the user equipment, the dropped UL transmission maynot be useful information for determining whether the channel for themedium between the user equipment and the base station is busy or idle.Therefore, when the base station performs the CWS update/adjustment foreach user equipment, it may consider performing the CWSupdate/adjustment based on whether the base station receives the PUSCHtransmitted by the user equipment. For example, when the user equipmenttransmits the PUSCH and the base station successfully decodes the PUSCH,the base station may reset the CWS of the corresponding user equipmentto the minimum value (i.e., CWmin) by determining that the response forthe PUSCH transmission is an ACK. In this case, the user equipmentdetermines that the channel between the user equipment and the basestation is idle, so that the user equipment may reset every CWp (e.g.,p={1, 2, 3, 4}), which may be set differently according to the channelaccess priority class, to the minimum value (i.e., (CWmin, p)).Meanwhile, when the base station fails to decode the correspondingPUSCH, the base station may double the CWS of the corresponding userequipment by determining that the response to the PUSCH transmission isa NACK and. In this case, the user equipment determines that the channelbetween the user equipment and the base station is busy, so that theuser equipment doubles the CWp (e.g., p={1, 2, 3, 4}) that may bedifferently set according to the channel access priority class. Inaddition, if the base station performs energy detection for the PUSCHtransmission through detection of the UL DM-RS, or if the PUSCH isscheduled with the SRS, the energy detection of the SRS may be performedto determine whether the PUSCH is transmitted.

When the base station manages the CWS of each user equipment accordingto a PUSCH decoding result, the base station may enable each userequipment to perform the CWS update/adjustment using a new dataindicator (NDI) included in a UL grant. The NDI is 1-bit informationindicating an initial-transmission/retransmission of the PUSCH based onwhether it is toggled based on an NDI value of the previous UL grant.For example, if an NDI value of the current UL grant is equal to the NDIvalue of the previous UL grant, the current UL grant indicates aretransmission of the PUSCH (i.e., decoding failure of the previousPUSCH). In addition, if the NDI value of the current UL grant is toggleddifferently from the previous value, the current UL grant indicates aninitial transmission of the PUSCH (i.e., the decoding success of theprevious PUSCH). Specifically, when the NDI on the UL grant received inthe n-th subframe from the base station is toggled so that transmissionof a PUSCH scheduled to the corresponding user equipment in the (n+4)-thsubframe indicates new data, at the time when the UL grant is received,the CWp for the corresponding user equipment may be reset, that is, thecurrent CWp may be set to the CW_min, p value. Unlike this, when the NDIreceived on the UL grant received in the n-th subframe from the basestation does not indicate the new data (i.e., when the NDI in the(n−4)-th UL subframe is not toggled to indicate retransmission of thePUSCH), it may perform LBT for transmission of the PUSCH in the (n+4)-thsubframe by doubling the current CWS (at the time of receiving the ULgrant). In addition, if the LBT using the CW_max value is repeatedly setto K times (e.g., K={1, . . . , 8}) by retransmission, CWp may be set tothe CW_min value. The value K may be designated to one value of {1, . .. , 8} by the base station.

Next, when the base station manages only a CWS for the base stationtransmission without information on the CWS of the user equipment andeach user equipment(s) manages its own CWS, each user equipment mayperform the CWS update/adjustment using New data indicator (NDI)information included in the UL grant transmitted from the base station.For example, when the NDI on the UL grant received in the n-th subframefrom the base station is toggled so that transmission of the PUSCHscheduled to the corresponding user equipment in the (n+4)-th subframeindicates the new data, at the time when the UL grant is received, theCWp for the corresponding user equipment may be reset, that is, thecurrent CWp may be set to the CW_min, p value. Unlike this, when the NDIreceived on the UL grant received in the n-th subframe from the basestation does not indicate the new data (i.e., when the NDI in the(n−4)-th UL subframe is not toggled to indicate retransmission of thePUSCH), it may perform the LBT for the transmission of the PUSCH in the(n+4)-th subframe by doubling the current CWS (at the time of receivingthe UL grant). In addition, if the LBT using the CW_max value isrepeatedly set to K times (e.g., K={1, . . . , 8}) by retransmission,CWp may be set to the CW_min value. The value K may be designated to onevalue of {1, . . . , 8} by the base station.

If the user equipment adjusts the CWS according to toggle of the NDIincluded in the UL grant, it may be considered to update/adjust the CWSdepending on whether the UL transmission on a reference subframe hasbeen successfully decoded to promptly adjust the CWS according to the ULchannel states. Here, the reference subframe may be defined as follows.

-   -   The reference subframe is defined as a starting transmission        subframe of the most recent UL transmission burst in which the        Cat-4 LBT procedure is expected to be used, and it refers to the        subframe in which the transmission of the UL DMRS or SRS from        the user equipment is detected by the base station and the PUSCH        is decoded.    -   The reference subframe may be defined as the starting        transmission subframe of the most recent UL transmission burst        in which the Cat-4 LBT procedure is expected to be used.    -   The reference subframe may be defined as the first subframe of a        reference scheduled burst in which the base station successfully        decodes at least one transport block on the LAA SCell. The        reference scheduled burst refers to the UL subframe(s) most        recently consecutively scheduled for the corresponding user        equipment. The reference scheduled burst is the UL subframe(s)        expected to initiate a UL transmission after a Cat-4 LBT, and        refers to the UL subframe(s) expected to complete transmission        before at least four subframes than a subframe in which the CWS        adjustment information (e.g., NDI) is transmitted.    -   The reference subframe may be defined as a (starting) subframe        of the most recent UL transmission burst successfully        transmitted by the user equipment.    -   The reference subframe may be defined as a (starting) subframe        of the most recent UL transmission burst successfully        transmitted, after the user equipment performs Cat-4.

When the base station successfully decodes the reference subframe (e.g.,PUSCH), the CWS may be reset by the user equipment. In addition, whenthe base station does not successfully decode the reference subframe(e.g., PUSCH), the CWS may be increased by the user equipment. When theCWS is defined for each of channel access priority classes, CWSp may bereset or increased to a CWSp value of the next higher allowed level forevery channel access priority classes. p is the channel access priorityclass (e.g., p={1, 2, 3, 4}).

When the PUSCH carries a plurality of transport blocks (TB) in thereference subframe (i.e., UL SU-MIMO) and at least one of the TB(s) inthe reference subframe are successfully decoded, CWS for each of thechannel access priority classes may be reset, and otherwise, the CWS maybe increased to a CWS value of the next higher allowed level of for eachof the channel access priority classes. The transmission success/failureof the user equipment with respect to the reference subframe may bedetermined by referring to the NDI value transmitted in the UL grant bythe base station. The NDI is set by each TB. Accordingly, if the NDI forat least one of the TB(s) for the reference subframe is toggled, the CWSmay be reset for every channel access priority classes, and otherwise(i.e., there is no toggled NDI), for every channel access priorityclasses, the CWS may be increased to the CWS value of the next higherallowed level. In other words, if any NDI is toggled in a subsequent ULgrant after and associated with the reference subframe (e.g., only oneof the two NDIs is toggled), the CWS may be reset to the minimum value,and the CWS may be increased if there is no toggled NDI. Whether the ULgrant is associated with a reference subframe of a previous ULtransmission burst may be determined based on whether or notHARQ-process ID of the reference subframe is the same as HARQ-process IDof a subframe scheduled by the UL grant (or uplink transmission (e.g.,PUSCH)). Since asynchronous HARQ may be applied to UL transmission onLAA SCell, whether the UL grant is associated with the referencesubframe of a previous UL transmission burst may be determined based onwhether the HARQ-process ID in the UL grant is the same as theHARQ-process ID used to schedule the reference subframe. Meanwhile, whenthe LBT using the CW_max value is repeatedly set to K times (e.g., K={1,. . . , 8}) by retransmission, only the CWp of the repeated channelaccess priority class may be set to the CW_min value. The value K may bedesignated to one value of {1, . . . , 8} by the base station.

Meanwhile, the base station may signal or indicate the user equipment alocation of the reference subframe within the reference scheduled burstthat the user equipment may use to update the CWS. For example, wheninformation indicating cat-4 LBT, as the LBT type to be performed by theuser equipment in UL transmission, is implicitly or explicitly signaledto the user equipment via the UL grant, information on the location ofthe reference subframe may be included in the corresponding UL grant.Even if no reference subframe is detected in the base station, the basestation may signal the information on the location of the referencesubframe to the user equipment.

For example, the number of bits may be determined according to thenumber of subframes scheduled for multi-subframe to inform the locationof the reference subframe in the reference scheduled burst with abitmap. As another example, the location of the reference subframe maybe indicated including a case where no reference subframe is detectedwith a bitmap regardless of the number of subframes scheduled formulti-subframe (e.g., 0000: no reference subframe, 1000: 1st subframe,0100: 2nd subframe, 0010: 3rd subframe, 0001: 4th subframe). Unlikethis, assuming that the maximum number of subframes that can bemulti-subframe scheduled is four, the location of the reference subframemay be designated with two bits. As another example, it is possible tosignal 5 states (e.g., no reference subframe, 1st subframe, 2ndsubframe, 3rd subframe, and 4th subframe) with 3 bits, including a casewhere any reference subframe is not detected.

When the user equipment receives the location of the reference subframefrom the base station, the user equipment may perform a UL transmission(e.g., PUSCH) in a subframe (e.g., the first UL subframe of fourconsecutive UL subframes) prior to a reference subframe (e.g., thesecond UL subframe of four consecutive UL subframes) in the referencescheduled burst. In this case, the base station may not receive the ULtransmission in the reference subframe even though the user equipmenthas transmitted it earlier. Therefore, the user equipment may determinethat a collision has occurred in the base station reception for the ULtransmission, and the user equipment may increase the CWS(s) for everychannel access priority classes (or LBT priority classes) (e.g., twice).

When the user equipment receives the location of the reference subframefrom the base station, the user equipment may perform a UL transmission(e.g., PUSCH) in a subframe (e.g., the third UL subframe of fourconsecutive UL subframes) after a reference subframe (e.g., the secondUL subframe of four consecutive UL subframes) in the reference scheduledburst. In this case, the user equipment may maintain the CWS(s) forevery channel access priority classes (or the LBT priority classes)without changing them. That is, the base station considers that the ULtransmission is received in the reference subframe even though the userequipment transmits it later and the CWS may be maintained byconsidering that it is not related to collision in the base stationreception for UL transmission.

When the user equipment receives the location of the reference subframefrom the base station, the user equipment may perform a UL transmission(e.g., PUSCH) in the same subframe (e.g., the first UL subframe of fourconsecutive UL subframes) in the reference scheduled burst. In thiscase, since the user equipment performs the UL transmission in thereference subframe and the base station successfully decodes at leastone transport block for the UL transmission of the reference subframe,the user equipment may determine that the base station successfullyreceives the UL transmission. Thus, the user equipment may reset theCWS(s) for every channel access priority classes (or the LBT priorityclasses) to a minimum value.

Meanwhile, if the user equipment is configured to reset the CWS orincrease it to the next higher allowed level in the cat-4 LBT based onthe NDI for the reference subframe, since asynchronous HARQ is appliedto UL transmission in LAA SCell, not synchronous HARQ, it is notguaranteed that the UL grant that may refer to the retransmission for ULtransmission (e.g., PUSCH) transmitted in the subframe n is transmittedin the subframe (n+4). Therefore, when the UL grant is not received inthe subframe (n+4), ambiguity arises as to whether the user equipmentshould reset the CWS or increase it to the next level for using the CWSfor the cat-4 LBT. To solve this problem, if the NDI for at least one ofthe TB(s) based on the NDI of the recently received UL grant is toggled,the user equipment resets the CWS for every channel access priorityclasses to CW_min, and otherwise, increases the CWS to a CWS value ofthe next higher allowed level for every channel access priority classes.In addition, when the LBT using the CW_max value is repeatedly set to Ktimes (e.g., K={1, . . . , 8}) by retransmission, only the CWp of therepeated channel access priority class may be set to the CW_min value.The value K may be designated to one value of {1, . . . , 8} by the basestation.

As described above, therefore, the base station may not distinguish thefollowing three cases in which the user equipment fails to transmit thePUSCH. Therefore, a method for classifying the following three cases anda method for adjusting the CWS according to the corresponding methodwill be described.

-   -   First, the case where the PUSCH may not be transmitted due to        not receiving the UL grant,    -   Second, the case where LBT fails before PUSCH transmission and        PUSCH may not be transmitted    -   Third, the case where LBT succeeds before PUSCH transmission but        PUSCH may not be transmitted (e.g., UL power limit case)

First, as an example of a method for distinguishing the first and secondcases, if LAA SCell is configured to receive cross-carrier schedulingfrom a cell of a licensed carrier, (E)PDCCH and PDSCH including the ULgrant for transmission of the UL PUSCH on the LAA SCell may besimultaneously transmitted in the downlink. In this case, when the basestation detects explicit HARQ-ACK feedback (including a case ofreceiving “ACK, NACK” or “ACK, NACK, NACK/DTX” or at least ACK or NACK)as feedback on the PDSCH rather than no transmission on a licensedcarrier or an unlicensed carrier, since it may be seen that (E)PDCCHscheduling PDSCH may be regarded as successful in the user equipment,the base station may determine that the user equipment has successfullyreceived the UL grant. Thus, in the first case, that is, the PUSCH maynot be transmitted because the UL grant is not received, it may beexcluded from the event to adjust (e.g., CWS increase) the CWS used toperform the UL LBT for transmission of the next PUSCH. When (E)PDCCHincluding the UL grant is transmitted from the cell of the licensedcarrier, since the first case may not be advantageous informing thestate of the channel collision for transmission of the UL PUSCH on theLAA SCELL, the base station may be excluded for adjusting the CWS forthe uplink transmission of the user equipment. That is, when the basestation may not receive (or detect) the PUSCH at the transmission timingof the PUSCH determined by the reception of the UL grant, the basestation may determine that the PUSCH is not transmitted due to thefailure of the PUSCH LBT and increase the CWS for the corresponding userequipment (e.g., twice).

The above contents may be identically applied to the case where theunlicensed carrier or LAA SCell is configured to self-carrierscheduling. When the (E)PDCCH and the PDSCH including the UL grant fortransmission of the UL PUSCH on the LAA SCell may be simultaneouslytransmitted on the downlink on the LAA SCELL, as feedback on the PDSCH,the explicit HARQ-ACK feedback (including a case in which one of “ACK,NACK” or “ACK, NACK, NACK/DTX” or at least ACK or NACK is detected),which is not a no transmission case, may be detected by the base stationon a licensed carrier or an unlicensed carrier. In this case, it may beseen that the reception of the (E)PDCCH for scheduling the PDSCH issuccessful in the user equipment. In addition, the base station maydetermine that the user equipment has successfully received the ULgrant. Thus, in the first case, that is, when the PUSCH may not betransmitted because the UL grant is not received on the unlicensedcarrier, it may be excluded from the event to adjust (e.g., CWSincrease) the CWS used to perform the UL LBT for transmission of thenext PUSCH. That is, when the base station may not receive (or detect)the PUSCH at the transmission timing of the PUSCH determined by thereception of the UL grant, the base station may determine that the PUSCHis not transmitted due to the failure of the PUSCH LBT and increase theCWS for the corresponding user equipment (e.g., twice).

Next, an implicit signaling method and an explicit signaling method willbe described as methods by which the base station may distinguishbetween the second and third cases.

First, as an implicit signaling method, when a CA is configured for apower limitation case of a user equipment, a PUSCH on an unlicensedcarrier may be dropped according to a transmission priority according toa channel type in different carriers and contents of channels. Thetransmission priority may follow the priority defined in the standard upto the existing 3GPP Rel-13 (e.g., PRACH>PUCCH>PUSCH withUCI>PUSCH>periodic SRS). Therefore, when transmission of channels (e.g.,PRACH, PUCCH, or PUSCH with UCI) having a higher priority than the PUSCHon the unlicensed carrier is detected in another carrier at transmissiontiming of the PUSCH according to the UL grant transmission, the basestation may regard the PUSCH on the unlicensed carrier as dropped due tothe power limitation state of the user equipment. In this case, thePUSCH not received on the unlicensed carrier may be excluded from theevent to adjust the CWS (e.g., CWS increase) used to perform UL LBT fortransmission of the next PUSCH. That is, although the LBT for the PUSCHhas succeeded (i.e., the channel is idle), even if the PUSCH is notreceived (or detected) in the base station at the transmission timing ofthe PUSCH according to the UL grant because the PUSCH may not betransmitted due to the power limitation state of the user equipment, thebase station may not double or increase the CWS of the correspondinguser equipment (i.e., maintain the CWS).

In addition, the above implicit signaling method may be configureddifferently in a case where the user equipment receives cross-carrierscheduling of the PUSCH and in a case where the user equipment receivesself-carrier scheduling of the PUSCH. In the case of the self-carrierscheduling, when it is determined that the UL grant has beensuccessfully received, the channel state may be considered/regarded tobe idle at the PUSCH transmission timing on the unlicensed carrier. Thatis, although the PUSCH LBT succeeds, even if the PUSCH is not received(or detected) at the base station at the transmission timing of thePUSCH according to the UL grant, in consideration that the PUSCH may notbe transmitted due to the power limitation state of the user equipment(i.e., the third case), the CWS of the corresponding user equipment maynot be doubled or increased from the previous CWS (i.e., maintain theCWS).

In the case of the cross-carrier scheduling, successful UL grantreception on the licensed carrier may not be considered as a method fordetermining the state of a channel at the PUSCH timing on an unlicensedcarrier. In this case, since it is difficult for the base station todetermine the second case and the third case, the base stationarbitrarily determine whether the second case or the third case to applythe CWS adjustment method. Alternatively, in order to configurate toobtain more channel opportunities, even if it is scheduled by a UL grantfrom a licensed carrier, in a case where the PUSCH is not received, amethod may be considered in which the CWS is configured to be doubled orincreased from the previous value.

Next, as an explicit signaling method, information on a PUSCH LBTfailure on the LAA SCELL or information on whether the PUSCH on the LAASCell is dropped due to power limitation may be included within thePUCCH/PUSCH of the licensed PCell or the PUCCH/PUSCH of the licensedSCell and transmitted. Alternatively, information on a PUSCH LBT failureon another LAA SCell or information on whether a PUSCH on the LAA SCellis dropped due to power limitation may be included in a PUSCH of the LAASCell set to be transmittable after LBT success and transmitted.

FIG. 18 illustrates a signal transmission process.

Referring to FIG. 18, after receiving a UL grant (e.g., UG #1) from abase station, a user equipment may transmit an n-th UL transmissionburst (e.g., UTB #1) (S1802). The UTB #1 includes one or more,preferably two or more, consecutively scheduled UL subframe(s), and aPUSCH may be transmitted for each UL subframe. The UTB #1 may betransmitted in an unlicensed band (e.g., an LTE-U cell) and may betransmitted based on a Cat-4 LBT procedure (i.e., Type 1 channelaccess). Then, the base station may transmit UL grant (e.g., UG #2) tothe user equipment (S1804). The UG #2 includes scheduling informationfor the (n+1)-th UL transmission burst (e.g., UTB #2), and the UTB #2includes one or more contiguously scheduled UL subframe(s). The UG #2includes PUSCH scheduling information for each UL subframe in the UTB#2, and each PUSCH scheduling information includes an NDI for each TB.The user equipment may transmit UTB #2 according to UG #2 (S1812). TheUTB #2 may also be transmitted in an unlicensed band (e.g., LTE-U cell)and may be transmitted based on the Cat-4 LBT procedure. Specifically,if channel of the unlicensed band is in an idle state during the ECCAdefer period, the user equipment further performs a random backoffwithin a CWS (S1810). The user equipment generates a random number Nequal to or less than the CWS (e.g., [0, q−1]) (S1808) and performsbackoff with the number of slots corresponding to the random number N(S1810). In this case, the size (i.e., CWS) of CW is adaptively changedbased on the NDI value of the UG #2 (S1806). The NDI value used foradjusting the CWS may be related to the UL transmission (i.e., PUSCH) ona reference subframe in the most recent UL transmission burst (i.e., UTB#1). Specifically, when at least one NDI is toggled with respect to theTB(s) transmitted on the reference subframe in the UTB #1, the CWS isreset to the minimum value, otherwise the CWS may be increased. Forexample, if multiple (e.g., two) TBs are transmitted on the referencesubframe and at least one NDI is toggled in a UL grant after andassociated with the reference subframe (e.g., only one of the two NDIsis toggled), the CWS may be reset to the minimum value. Sinceasynchronous HARQ is applied to UL transmission in LAA SCell, in the ULtransmission, whether the UL grant is associated with the referencesubframe of the previous UL transmission burst may be confirmed using aHARQ-process ID. For example, when the UL grant having the HARQ-processID used for the scheduling of the reference subframe is received afterthe reference subframe (or when the HARQ-process ID of the referencesubframe and the HARQ process ID of the subframe scheduled by the ULgrant are the same), and when at least one of the NDI values in the ULgrant are toggled, the CWS may be reset to the minimum value. On theother hand, if the UL grant associated with the reference subframe isnot received, or the UL grant associated with the reference subframe isreceived but the NDI is not toggled on all TBs, the CWS may beincreased. When CWS increases, CWS may be doubled or increasedexponentially between the minimum value (i.e., CW_min) and the maximumvalue (i.e., CW_max) or increased to the maximum value.

The method described above based on multi-subframe scheduling may besimilarly applied to the case of single subframe scheduling.

Next, a signaling method for the LBT parameter for adjusting the CWS atperforming UL LBT for UL PUSCH transmission by the user equipment willbe described.

When a base station informs a user equipment of a UL LBT parameter,since the base station may difficult to recognize the channel accesspriority class for the traffic transmitted by the user equipment,notifying CWS of every channel access priority classes to the userequipment may be a large signaling overhead. Also, when each channelaccess priority class follows the channel access priority class (DLchannel access priority class) used in the DL, as shown in Table 6, therange of allowed CWp size is large, so that related signaling overheadmay be increased.

TABLE 6 Channel Access Priority Class (p) m_(p) CW_(min, p) CW_(max, p)T_(mcot, p) allowed CW_(p) sizes 1 1 3 7 2 ms {3, 7} 2 1 7 15 3 ms {7,15} 3 3 15 63 8 or 10 ms {15, 31, 63} 4 7 15 1023 8 or 10 ms {15, 31,63, 127, 255, 511, 1023}

In addition, Table 7 may be used as an LBT parameter for the UL channelaccess priority class.

TABLE 7 LBT priority class n CWmin CWmax MCOT Set of CW sizes 1 2 3 7 2ms {3, 7} 2 2 7 15 4 ms {7, 15} 3 3 15 1023 6 ms (see note 1) or {15,31, 63, 127, 10 ms (see note 2) 255, 511, 1023} 4 7 15 1023 6 ms (seenote 1) or {15, 31, 63, 127, 10 ms (see note 2) 255, 511, 1023} Note 1,Note 2

Note1: The maximum channel occupancy time (MCOT) of 6 ms may beincreased to 8 ms by inserting one or more gaps and the minimum durationof a pause due to the gap should be 100 us. The maximum duration lengthbefore including the gap should be 6 ms. The gap duration is notincluded in the channel occupancy time.

Note2: If the absence of any other technology (e.g., Wi-Fi) on the samecarrier is guaranteed, the MCOT for LBT priority classes 3 and 4 may beup to 10 ms, otherwise, the MCOT for LBT priority classes 3 and 4 is asspecified in Note 1.

Therefore, in order to inform the CW size among the LBT parameters thatthe base station may inform the user equipment, a method for reducingthe signaling overhead and a method for adjusting the CWS according tothe signaling overhead will be described.

First, as the base station informs the user equipment of a common valuefor the CWS regardless of the channel access priority class, the userequipment receiving the common value may perform an LBT that performs abackoff operation using the CWS corresponding to a common valueaccording to the channel access priority class to be transmitted. Inother words, the base station determines whether the CWS is doubled orincreased based on the reception of the PUSCH transmitted from the userequipment, and informs the user equipment of a common value with theparameters for the LBT, regardless of the channel access priority class,the user equipment receiving the common value sets the CWS according tothe common value of the LBT of the PUSCH to be transmitted to performsthe LBT, and transmits the PUSCH according to the success of the LBT. Inthe case of receiving a common value through the UL grant, when thecommon value is 0, the LBT may be performed with the minimum value ofthe CW size of the channel access priority class for the PUSCH to betransmitted, and when the common value is 1, LBT may be performed bysetting the minimum value of CW size to the next level value. As acommon value is applied according to sizes of CWp allowed in eachchannel access priority class, as in DL, when the maximum CWmax, p valuein the channel access priority class is repeatedly set to K times, theCWp value may be set to the CWmin, p value in the channel accesspriority class. Here, K may be selected from {1, 2, . . . , 8} by thebase station. K may be indicated to the user equipment via RRCsignaling.

When DL channel access priority class 4 is used, 6 is indicated as thecommon value for CWS, and in a case where the next PUSCH transmission isintended for transmission with channel access priority class 1, inconsidering that the maximum CWS is repeated 6 times, according to thecondition that if it is repeatedly set to K times by the base station,CWp value should be set to CWmin, p value in channel access priorityclass, the CWS of the PUSCH for the corresponding channel accesspriority class may be determined. A method may be considered in whichwhen K is configured to 6, CWp may be set to the minimum value CWS, andif K is configured to 4, it is configured to the CWp maximum value, andsince the common value is larger than the set value K, CWp is configuredto the minimum value CWS.

Furthermore, as another method, as the level of allowed CWp size for ULPUSCH transmission is configured to the same number of levels (e.g., oneof {2, 3, 4, . . . , 8 steps}) for every channel access priorityclasses. In addition, the base station informs the user equipment of thecommon value for the CWS regardless of the channel access priorityclass. Then, the user equipment receiving the common value may performan LBT that performs backoff using the CWS corresponding to the commonvalue according to a channel access priority class to be transmitted.This may be a method in which the increase or reset of the CWS withrespect to the adjustment of the CWS according to each channel accesspriority class is controlled to be the same by the common value and thesignaling overhead for CWS indication is reduced. In other words, in thecase of receiving the common value of a condition in which the CWSincreases for every channel access priority classes, the CWS isincreased to the next higher allowed value regardless of the channelaccess priority class to be transmitted from the user equipment. Inaddition, even in the case of receiving the common value of the resetcondition in the CWS reset or satisfying the reset condition byrepeating K times, the corresponding CWS for every channel accesspriority class is reset regardless of the channel access priority class.This may be considered as a method for reducing the signaling overheadfor CWS among the LBT parameters transmitted in the UL grant. As oneembodiment below, when the channel access priority class used in the DLis based on the following method, a method for setting a level of theallowed CWp size to two levels may be used. In the corresponding case, asignaling overhead of a common value indicating CWS is sufficient forone bit.

TABLE 8 Channel Access Priority Class (p) allowed CW_(P) sizes 1 {3, 7}2 {7, 15} 3 {15, 31} 4 {31, 63}

If Modified to a more general allowed CWp size representation, it may beas follows.

TABLE 9 Channel Access Priority Class (p) allowed CW_(p) sizes 1 {A, B}2 {C, D} 3 {E, F} 4 {G, H}

Here, B, C, D, E, F, G, and H values may be set to values satisfying thecondition A<B=<C<D=<E<F=<G<H, and B, D, F, and H values may be set asthe maximum CW size value of the corresponding channel access priorityclass. For example, when the maximum allowed CW size uses the value usedin the DL, each of B, D, F, and H may have one value of {7, 15, 31, 63,127, 255, 511, 1023}.

As another embodiment, if the UL transmission is configured to use asmaller CW size than the DL transmission. For example, when the maximumallowed CW size is configured to {3, 4, 5, 6} or {3, 4, 5, 6, 7}, evenwhen having the maximum CWS defined by the value of one of {3, 4, 5, 6}or one of {3, 4, 5, 6, 7}, the allowed CWp size level for UL PUSCHtransmission may be set to the same number of levels for every channelaccess priority classes.

Table 10 is one example, and a method for setting an allowed CWp sizelevel to two levels may be used.

TABLE 10 Channel Access Priority Class (p) allowed CW_(p) sizes 1, 2 {A,B} 3, 4 {C, D}

Here, B, C, and D values may be set to values satisfying the conditionA<B=<C<D, and B and D values may be set to the maximum CW size value ofthe corresponding channel access priority class. For example, if themaximum allowed CW size is configured to {3, 4, 5, 6} or {3, 4, 5, 6,7}, it is possible to set each of B and D to one of {3, 4, 5, 6} or oneof {3, 4, 5, 6, 7} as the maximum allowed CW size.

Referring to FIG. 9, B, C, D, E, F, G, and H values may be set to valuessatisfying the condition A<B=<C<D=<E<F=<G<H, and B, D, F, and H valuesmay be set to the maximum CW size value of the corresponding channelaccess priority class. For example, if the maximum allowed CW size isconfigured to {3, 4, 5, 6} or {3, 4, 5, 6, 7}, it is possible to seteach of B, D, F, and H to one of {3, 4, 5, 6} or one of {3, 4, 5, 6, 7}as the maximum allowed CW size.

When the base station performs the scheduling to the user equipment asshown in FIGS. 19 to 20 and configures the reference subframe forupdating the CWS by the user equipment. In this case, the user equipmentperforms the UL LBT for the reference subframe according to thescheduling information transmitted in the UL grant from the basestation. Then, when the LBT succeeds, the use equipment performs ULtransmission in the UL reference subframe. However, even though the userequipment performs the UL transmission, a case where the base stationfails to detect the UL transmission, due to the channel interferencecondition of the unlicensed band used by the LAA SCell, may occur. Inthis case, the base station may not accurately identify whether the ULtransmission of the scheduled UL subframe fails to perform transmissiondue to UL LBT failure of the user equipment, due to transmission failureat the user equipment, or because the user equipment miss the UL grantfrom the base station, or whether the base station may not detect it dueto channel interference in the corresponding subframe. Especially, ifthe base station fails to detect the reference subframe despite thetransmission of the reference subframe from the user equipment, the CWSshould be increased, but if the base station and the user equipmentdetermine the reference subframe differently each other, the CWS may bereset even though it is an increase condition of the CWS. Alternatively,the opposite case may occur. Accordingly, by solving the mismatchproblem of the reference subframe between the base station and the userequipment for adjusting the CWS and setting to have the sameunderstanding between the base station and the user equipment, indetermining the CWS for the UL LBT performed by the user equipment, amethod for configuring the base station and the user equipment torecognize whether the reference subframe of the UL transmission burstreceived at the base station is same as the reference subframetransmitted by the user equipment will be described.

When assuming that a reference subframe is a starting transmissionsubframe of a UL transmission burst transmitted from a user equipment byperforming cat-4 LBT, the following description is a method forindicating the starting transmission subframe of the UL transmissionburst in the user equipment and a method for configuring a base stationto recognize whether the first subframe of a UL transmission burstreceived by the base station is the first subframe transmitted by theuser equipment.

FIG. 21 is a diagram showing a structure of a UL radio frame, a ULsubframe, and a UL slot in LTE. In the LTE, a cyclic-shift index of asequence of a reference signal (e.g., UL DMRS) within the UL subframe isdetermined by a value set by the cyclic-shift index of the UL DMRS inthe UL grant transmitted from a base station to a user equipment and RRCsignaling, and a function of the slot index. The cyclic shift valuedetermined by RRC signaling during a certain time interval is the same,and since the cyclic shift index value determined by the UL grant isconstant within a subframe, the cyclic shift value of the UL DMRS in thesubframe may be determined to be a different value depending on the slotindex.

Method P) as a method different from a method of using the cyclic-shiftindex of the UL DM-RS sequence transmitted in the UL subframetransmitted at the first in the UL transmission burst transmitted afterthe UL LBT based on the slot index used in the legacy, a method fortransmitting a UL DM-RS sequence using the following methods P-1 to P-3may be considered. Therefore, as the base station performs detection ofthe UL DMRS as many as twice at the time of the PUSCH detection for eachsubframe of the UL transmission burst scheduled by the base station, thebase station determines whether each subframe of the received ULtransmission burst is the first successfully transmitted subframe orwhether there is the first successfully transmitted subframe prior totransmission of the corresponding subframe.

Method P-1) as one embodiment, unlike the legacy method, the userequipment switches a cyclic shift index of a UL DM-RS sequencetransmitted in the UL subframe transmitted at the first in the ULtransmission burst to a cyclic shift index of a UL DM-RS transmitted ineach slot of the UL subframe transmitted at the first transmission, thatis, switches the first slot index and the second slot index, so that theuser equipment transmits the UL subframe including the UL DM-RS bysetting the cyclic shift of the UL DM-RS sequence transmitted in thefirst slot based on the second slot index and the cyclic shift of theDMRS sequence transmitted in the second slot based on the first slotindex.

As the user equipment informs whether the corresponding UL subframe isthe first UL subframe of the UL transmission burst scheduled from thebase station, through indicating that the cyclic shift index of the ULDM-RS is switched between the slots, when the user equipment transmitsthe UL subframe to the base station, this may be used as a method forpreventing a mismatch of the user equipment and the base station for thestarting transmission UL subframe.

For contiguous UL subframes of UL transmission bursts scheduled by thebase station, the base station performs two detections based on the ULDM-RS generated by two different schemes (i.e., switching or noswitching of the UL DM-RS cyclic shift value between the slots) untilthe PUSCH detection of the UL subframe. Then, when the UL PUSCH isdetected by the switched UL DM-RS, the transmission of the correspondingsubframe may be determined as the UL subframe at the starting of the ULtransmission burst form the user equipment. In this case, depending onthe success of PUSCH decoding in the starting UL subframe, the basestation may signal the user equipment through signaling (e.g., UL grant,common control channel, common PDCCH) a reset of the CWS or that the CWSincreases with a next higher allowed value. Unlike this, if the UL PUSCHis detected by the non-switched UL DM-RS at the base station, the basestation determines that the transmission of the corresponding subframeis not the transmission of the first UL subframe of the UL transmissionburst from the user equipment and the first UL subframe of the ULtransmission burst in the user equipment is transmitted from the userequipment but the first UL subframe may not be detected at the basestation due to the interference condition of the channel, so that thebase station may signal the user equipment through signaling (e.g., ULgrant, common control channel, common PDCCH) to increase the CWS to thenext higher allowed value.

Method P-2) A method of setting the cyclic shift index of the UL DM-RSsequence in the first slot and the cyclic shift index of the UL DM-RSsequence in the second slot according to the same slot index may beconsidered. There may be a method of setting the cyclic shift index ofthe UL DM-RS sequence to be the same based on the index of the firstslot of the UL subframe to be transmitted, and there may be a method ofsetting the same cyclic shift index of the UL DM-RS sequence based onthe index of the second slot.

As the user equipment informs whether the UL subframe is the starting ULsubframe of the UL transmission burst scheduled from the base stationwhen the user equipment transmits the UL subframe to the base stationthrough indicating that the cyclic shift index of the UL DM-RS isswitched between the slots, this may be used as a method for preventinga mismatch of the user equipment and the base station for the startingtransmission UL subframe.

For contiguous UL subframes of UL transmission bursts scheduled by thebase station, the base station performs two detections based on the ULDM-RS generated by the two different schemes (i.e., based the same slotindex for the UL DMRS cyclic shift value between the slots or based oneach slot index for the UL DM-RS cyclic shift value) until the PUSCHdetection of the UL subframe. Then, when the UL PUSCH is detected by theUL DM-RS generated by the value of the same slot index of the UL DM-RScyclic shift value between the slots, the transmission of thecorresponding subframe may be determined as the UL subframe at thestarting of the UL transmission burst from the user equipment. In thiscase, depending on the success of PUSCH decoding in the starting ULsubframe, the base station may signal the user equipment throughsignaling (e.g., UL grant, common control channel, common PDCCH) a resetof CWS or that the CWS increases with a next higher allowed value.Unlike this, if the UL PUSCH is detected in the base station by the ULDM-RS generated by the value set based on the slot index, the basestation determines that the transmission of the corresponding subframeis not the transmission of the first UL subframe of the UL transmissionburst from the user equipment and the first UL subframe of the ULtransmission burst in the user equipment is transmitted from the userequipment but the first UL subframe may not be detected at the basestation due to the interference condition of the channel, so that thebase station may signal the user equipment through signaling (e.g., ULgrant, common control channel, common PDCCH) to increase the CWS to thenext higher allowed value.

Method P-3) A method for transmitting a pre-defined cyclic shift indexof UL DM-RS sequence based on the pre-defined index of the cyclic shiftof the UL DM-RS previously set for a base station and a user equipmentby applied to the UL DM-RS of a UL subframe to be transmitted at thefirst by the user equipment may be considered.

Method Q) as a method different from a method for using the cyclic-shiftindex of the sequence of the UL DM-RS transmitted in the UL subframe(s)excluding the UL subframe transmitted at the first in the ULtransmission burst transmitted after the UL LBT based on a slot indexusing in a legacy, by generating a UL DM-RS sequence by using thefollowing methods Q-1 to Q-3 to transmit, it is possible to distinguishbetween the starting transmission of the UL transmission burst at thebase station and the non-starting transmission.

Method Q-1) as the setting of the cyclic-shift index of the UL DM-RSsequence transmitted to the UL subframe excluding the first UL subframetransmitted in the UL transmission burst is different from the legacymethod, the user equipment switches the cyclic shift index of the ULDMRS transmitted in each slot between the slots, that is, switches thefirst slot index and the second slot index, so that the user equipmenttransmit the UL subframe including the UL DMRS by setting the cyclicshift of the DMRS sequence of the UL DMRS transmitted in the first slotbased on the second slot index and the cyclic shift of the DMRS sequenceof the UL DMRS transmitted in the second slot based on the first slotindex.

Method Q-2) In the UL subframe(s) except the first UL subframetransmitted in the UL transmission burst, a method of setting the cyclicshift index of UL DMRS sequence in first slot and the cyclic shift indexof the UL DMRS sequence in the second slot by the user equipmentaccording to the same slot index may be considered. There may be amethod of setting the cyclic shift index of the UL DMRS sequence to bethe same based on the index of the first slot of the UL subframe to betransmitted, and there may be a method of setting the same cyclic shiftindex of the UL DMRS sequence based on the index of the second slot.

Method Q-3) In the UL subframe(s) except the first UL subframetransmitted in the UL transmission burst, a method for transmitting acyclic shift index of a pre-defined UL DMRS sequence based on apre-defined index of the cyclic shift of the UL DMRS previously set fora base station and a user equipment by applied to the UL DMRS of a ULsubframe to be transmitted at the first by the user equipment may beconsidered.

FIG. 22 illustrates a method for determining a CWS in a subframe inwhich Cat-4 should be performed for UL transmission. Specifically, itillustrates a case where each UL scheduled subframe of the most recentUL transmission burst has a gap between consecutive subframes and isscheduled by each UL grant (i.e., FIG. 20(a)), a case where schedulingis performed with a gap between consecutive UL subframes scheduled by amulti-subframe scheduling from one DL subframe (i.e., FIG. 20(b)), and acase where scheduling is performed with a gap between UL subframesscheduled by a plurality of UL grants from one DL subframe (i.e., FIG.20(c)). In these cases, each UL subframe performing each cat-4 LBT maybe regarded as a UL transmission burst due to a gap between ULsubframes. As shown in FIG. 20, if there is a gap between scheduled ULsubframes, in determining the CWS for performing cat-4 for the next ULtransmission, the most recent UL transmission burst performing cat-4 asthe reference subframe may be an A subframe (e.g., UL SF #(n+4+k)), a Bsubframe (e.g., UL SF #(n+5+k)), or a C subframe (e.g., UL SF #(n+6+k))in FIGS. 20(a), 20(b) and 20(c). Here, since a subframe that hasperformed each cat-4 transmitted lastly may be the subframe of the ULburst most recently, in this case, even if it is the UL subframe thatstarts first among the scheduled subframes due to LBT success in thepreceding cat-4 LBT, by informing the starting subframe of the UL burstby using Methods P-1, P-2, P-3 and Methods Q-1, Q-2 and Q-3 in thecorresponding subframe, it is difficult to solve the reference subframemismatch for adjusting the CWS for the next UL transmission between thebase station and the user equipment. In such a case, detection of the ULDMRS and the PUSCH twice in the base station may increase only thedetection complexity of the base station. Therefore, in a case where thebase station configures the user equipment to perform scheduling with aUL gap, a method in which the base station signals the user equipment tonot perform the modification transmission of the UL DMRS sequence in theuser equipment, that is, Methods P-1, P-2, P-3 and Methods Q-1, Q-2, andQ-3 may be considered. As the signaling method, for example, it ispossible to indicate through the UL grant, the common control channel orthe common PDCCH. As shown in FIG. 19, in a case where the base stationperforms the scheduling for the UL transmission burst without a gap, thebase station may configure the user equipment to use Methods P-1, P-2,and P-3 and Methods Q-1, Q-2, and Q-3 to solve the mismatch between thebase station and the user equipment for the reference subframe. Further,as shown in FIG. 20, in a case where the base station schedules the ULtransmission burst with a gap, the base station may signal the userequipment not to perform Methods P-1, P-2, and P-3 and Methods Q-1, Q-2,and Q-3 so as to reduce the number of blind detection times at the basestation.

Embodiment 1: Channel Access for Uplink Multi-Carrier Transmission

When a plurality of LAA SCells are configured, the following channelaccess method is used as a method for a base station to access a channelfor downlink multi-carrier transmission.

-   -   Multi-carrier channel access type A (i.e., Type-A): With regard        to each set (i.e., carrier set) which is a combination of        carriers through which the base station intends to perform        transmissions on the LAA SCell, a single-carrier channel access        procedure using cat-4 LBT may be independently performed for        each carrier. Thereafter, according to the determination of the        base station, a self-defer time that does not reduce the backoff        counter is used in a specific carrier, so that a transmission        time point is matched between multiple carriers.    -   Multi-carrier channel access type B (i.e., Type-B): Similar to        the scheme used in Wi-Fi, one carrier (c_j) among the carriers        intended to be transmitted by the base station is randomly        selected or the carrier (cj) is selected not to be changed at        least for one second, and channel access using the cat-4 LBT is        performed on the carrier (c_j). When channel access on the        carrier (c_j) successful, channel sensing is performed by at        least T_mc=25 us on other carriers (c_i) (ij) immediately before        the transmission time of the carrier that succeeded in the        channel access. In this case, the base station performs        multi-carrier transmissions including other carriers when the        channel is idle for the T_mc.

In a scheme for transmitting multiple carriers through a downlink,carriers through which the base station intends to transmit signalsbasically perform channel access by assuming a cat-4 LBT having abackoff. However, in the case of the channel access type B, the cat-4LBT may be performed in the specific carrier determined by the basestation and simultaneous transmission with the carrier in which thecat-4 LBT is performed may be performed on other carriers through thechannel sensing of 25 us interval. If the cat-4 LBT fails in thespecific carrier determined by the base station, transmission is notperformed on all the multiple carriers regardless of the result ofsensing in the other carriers.

However, in case of the uplink in which the user equipment performstransmission to the base station, the base station informs, through theUL grant, the user equipment of the LBT type that should be performed bythe user equipment. The LBT type may be, for example, (i) the cat-4 LBT,i.e., the type 1 channel access, or (ii) the cat-2 LBT (e.g., LBT basedon 25 us CCA only) that performs only channel sensing of a singleinterval, i.e., the type 2 channel access. Therefore, according to theLBT type indication of the base station, there may be a case where theLBT type in all carriers in which the user equipment performs uplinktransmission (e.g., PUSCH) is not cat-4 LBT. That is, the cat-4 LBT maybe indicated on some carriers and the cat-2 LBT may be indicated onanother carrier among the carriers through which the base stationintends that the user equipment to perform the transmission.

Hereinafter, a channel access method for a user equipment to transmitmultiple carriers and an uplink transmission method therefor will bedescribed. In this specification, transmitting a carrier meanstransmitting a signal (e.g., PUSCH) through or on the carrier. Inaddition, the carrier means a carrier (i.e., unlicensed carrier) (e.g.,LAA SCell) operating in the unlicensed band unless otherwise specified.Also, multi-carrier transmission in this specification refers to asignal transmission operation when multiple carriers are simultaneouslyscheduled on the LAA SCell(s). In actual signal transmission, accordingto the channel access method, signals may be transmitted only on somecarriers constituting multiple carriers, and signal transmission onother some carriers may be dropped.

FIG. 23 illustrates that a user equipment performs UL transmissions onmultiple carriers in the case where the base station independentlyindicates different UL LBT types to each carrier via the UL grant(s). Itis assumed that a self-carrier scheduling is performed.

First, it can be considered to reuse the type B-scheme used formulti-carrier channel access in the downlink for an uplink multi-carrieraccess scheme. In this case, when the base station has a plurality ofcarriers indicating the cat-4 LBT through the UL grant to the userequipment, and there are a plurality of carriers in which the userequipment is indicated to perform the cat-4 LBT based on the UL grantreceived from the base station the user equipment needs to select one ofthe carriers for which cat-4 LBT is indicated. It is to apply the schemein which the cat-4 LBT is performed on only one carrier and transmissionon the remaining carriers are allowed only by the sensing of Tmc (e.g.,25 us) in the type-B scheme. The following method can be used as amethod for selecting one of the carriers that the user equipment shouldperform cat-4 LBT.

First, through the base station signaling, the user equipment may selectone of the carriers to perform the cat-4 LBT. In this regard, the basestation may define the carrier in which the cat-4 LBT should beperformed and assign (via a UL grant for the carrier) the carrier to theuser equipment. However, in this case, if the user equipment misses thecorresponding UL grant, the user equipment cannot perform a channelaccess for multi-carrier transmission. Therefore, the base station maydesignate the priority value of the carrier in which the cat-4 LBTshould be performed and signal the value to the user equipment.Specifically, the base station may indicate the priority value of thecorresponding carrier to the user equipment via the UL grant(hereinafter, referred to as cat-4 LBT UL grant) indicating (each) cat-4LBT. Accordingly, the user equipment identifies the value indicated asthe priority by the base station and performs the cat-4 LBT first on thecarrier(s) having the highest priority. If the cat-4 LBT is successful,the user equipment senses for Tmc (e.g., 25 us) on other carriersimmediately before the transmission and may perform UL transmission(e.g., PUSCH) on multiple carriers simultaneously when the channel isbusy. Accordingly, even if the user equipment misses the UL grant forthe carrier set to the highest priority by the base station, the userequipment may perform the cat-4 LBT for UL transmission according to thenext higher priority value.

A method for selecting one of the carriers signaled that a cat-4 LBTshould be performed by the user equipment according to a predefined rulebetween the base station and the user equipment is as follows.

1) A carrier with the smallest (carrier/cell) index among the carriersfor which cat-4 LBT is indicated may be selected. That is, the userequipment performs cat-4 LBT only for the carrier having the smallestindex among the carriers for which the cat-4 LBT UL grant is received.In addition, the user equipment may sense at least for Tmc on theremaining carrier(s) immediately before the transmission and perform ULtransmission when the channel is idle. The present invention is alsoapplicable to a case where the user equipment misses the UL grant byselecting a carrier based on the received UL grant of the userequipment. In this specification, the cat-x LBT UL grant refers to theUL grant indicating cat-x LBT (e.g., x=2, 4).

2) A carrier with the largest CWS (i.e., maximum CWS) among the carriersfor which cat-4 LBT is indicated may be selected. That is, the userequipment performs cat-4 LBT only for the carrier having the largest CWSamong the carriers for which the cat-4 LBT UL grant is received. Inaddition, the user equipment may sense at least for Tmc on the remainingcarrier(s) immediately before the transmission and perform ULtransmission when the channel is idle. Accordingly, coexistence withWi-Fi may be guaranteed as much as possible. Further, the presentinvention is also applicable to a case where the user equipment missesthe UL grant by selecting a carrier based on the received UL grant ofthe user equipment.

3) A carrier with the smallest CWS (i.e., minimum CWS) among thecarriers for which cat-4 LBT is indicated may be selected. That is, theuser equipment performs cat-4 LBT only for the carrier having thesmallest CWS among the carriers for which the cat-4 LBT UL grant isreceived. In addition, the user equipment may sense at least for Tmc onthe remaining carrier(s) immediately before the transmission and performUL transmission when the channel is idle. Accordingly, it is possible tomaximally guarantee the UL transmission on the LAA SCell which performsscheduling-based channel access unlike Wi-Fi while allowing coexistencewith Wi-Fi. Further, the present invention is also applicable to a casewhere the user equipment misses the UL grant by selecting a carrierbased on the received UL grant of the user equipment.

4) A carrier with the largest random backoff counter (i.e., maximumbackoff counter) among the carriers for which cat-4 LBT is indicated maybe selected. That is, the user equipment performs cat-4 LBT only for thecarrier having the largest random backoff counter among the carriers forwhich the cat-4 LBT UL grant is received. In addition, the userequipment may sense at least for Tmc on the remaining carrier(s)immediately before the transmission and perform UL transmission when thechannel is idle. Accordingly, coexistence with Wi-Fi may be guaranteedas much as possible. Further, the present invention is also applicableto a case where the user equipment misses the UL grant by selecting acarrier based on the received UL grant of the user equipment.

5) A carrier with the smallest random backoff counter (i.e., the minimumbackoff counter) among the carriers for which cat-4 LBT is indicated maybe selected. That is, the user equipment performs cat-4 LBT only for thecarrier having the smallest random backoff counter among the carriersfor which the cat-4 LBT UL grant is received. In addition, the userequipment may sense at least for Tmc on the remaining carrier(s)immediately before the transmission and perform UL transmission when thechannel is idle. Accordingly, it is possible to maximally guarantee theUL transmission on the LAA SCell which performs scheduling-based channelaccess unlike Wi-Fi while allowing coexistence with Wi-Fi. Further, thepresent invention is also applicable to a case where the user equipmentmisses the UL grant by selecting a carrier based on the received ULgrant of the user equipment.

FIG. 24 illustrates an uplink multi-carrier transmission operation atthe time of LBT failure in a cat-4 LBT carrier(s) when the base stationseparately indicates the different UL LBT types for each carrier via theUL grant(s). It is assumed that a self-carrier scheduling is performed.

Referring to FIG. 24, even when the UL LBT fails in the carrier(s) inwhich the cat-4 LBT is performed, it is possible to performmulti-carrier transmission only using carriers in which cat-2 LBT isperformed when the UL LBT is successful in the carriers in which thecat-2 LBT is performed. In the case of the multi-carrier channel accesstype B in the downlink, if the cat-4 LBT fails in the specific carrierdesignated by the base station at the time of channel access of multiplecarriers, the LBT is not performed in the other carrier(s). Further,even if the LBT in the other carrier(s) is performed in advance,multi-carrier transmission not including the carrier in which the cat-4LBT is performed is not available regardless of the channel sensingresult. However, in the uplink case, UL LBT type (or UL channel accesstype) of each carrier is indicated by the UL grant(s) transmitted fromthe base station. In this case, an LBT failure may occur depending onthe interference condition or the channel condition in the carrier inwhich cat-4 LBT is performed as shown in FIGS. 23-24. However, in thecase of the carrier for which cat-2 LBT is indicated to be performedfrom the base station, uplink transmission on the corresponding carriermay be possible according to whether the cat-2 LBT is successful.Therefore, irrespective of the success or failure of the cat-4 LBT, itis possible to perform uplink transmission by allowing channel access inthe carrier for which cat-2 LBT is indicated, according to the successof the LBT. That is, channel access of the carrier(s) for which cat-4LBT is indicated and channel access of the carrier(s) for which cat-2LBT is indicated are independently managed. Thus, the success or failureof cat-4 LBT affects only the channel access/multi-carrier transmissionof the carrier(s) for which cat-4 LBT is indicated, and does not affectthe channel access/multi-carrier transmission of the carrier(s) forwhich cat-2 LBT is indicated. On the other hand, the success or failureof cat-2 LBT affects only the carrier on which the cat-2 LBT is actuallyperformed, and does not affect other carriers.

FIG. 24 illustrates a case where a single subframe is scheduled throughone UL grant. However, even when a multi-subframe is scheduled throughone UL grant as shown in FIG. 25, the UL channel access according to thepresent invention may be also applied in the same manner. Also, the ULchannel access according to the present invention may be similarlyapplied to the case where multiple subframes are scheduled through ULgrants transmitted from different downlink subframes as shown in FIG.26. Also, the UL channel access according to the present invention maybe similarly applied to the case where each UL scheduled subframe of theUL transmission burst is scheduled by the UL grant(s) of one DL subframeas in FIG. 27.

FIG. 25 illustrates that a user equipment performs UL transmission onmultiple carriers in the case where the base station independentlyindicates different UL LBT types for each carrier for multiple subframesvia UL grant(s). It is assumed that a self-carrier scheduling isperformed.

FIG. 26 illustrates that a user equipment performs UL transmissions onmultiple carriers in the case where the base station schedules multiplesubframes through the UL grant(s). Specifically, FIG. 26 shows a case ofindicating UL LBT type that may be the same or different for eachcarrier and different UL subframe, while transmitting UL grant(s) fromdifferent downlink subframes for each subframe of the multiplesubframes. It is assumed that a self-carrier scheduling is performed.

Referring to FIG. 26, the number of multiple carriers that can betransmitted according to the UL transmission time and the success of theLBT performed before each subframe transmission time may be changed foreach subframe. In the case of the cat-4 LBT being performed in thesubframe of the carrier set to perform the cat-4 LBT, if the channelaccess type of the multi-carrier set to be executable by the userequipment is signaled as the type-B, the LBT in other carriers exceptthe carrier in which cat-4 LBT is performed may perform sensing forTmc=25 us (i.e., sensing the Tmc immediately before the LBT completiontime in the carrier in which the cat-4 LBT is performed) to perform ULtransmission in multiple carriers.

FIG. 27 illustrates that a user equipment performs UL transmissions onLAA Scell(s) on multiple carriers in the case where the base stationschedules multiple subframes through the UL grant(s). Specifically, FIG.27 shows a case of indicating UL LBT type that may be the same ordifferent for each carrier and different UL subframe, while transmittingUL grant(s) from the same downlink subframes or different downlinksubframes for each subframe of the multiple subframes. It is assumedthat a self-carrier scheduling is performed.

Referring to FIG. 27, the embodiment is the same as that described inFIG. 26 except that multiple subframes are scheduled through one ULgrant. That is, the number of multiple carriers that can be transmittedaccording to the UL transmission time and the success of the LBTperformed before each subframe transmission time may be changed for eachsubframe. In the case of the cat-4 LBT being performed in the subframeof the carrier set to perform the cat-4 LBT, if the channel access typeof the multi-carrier set to be executable by the user equipment issignaled as the type-B, the LBT in other carriers except the carrier inwhich cat-4 LBT is performed may perform sensing for Tmc=25 us (i.e.,sensing the Tmc immediately before the LBT completion time in thecarrier in which the cat-4 LBT is performed) to perform UL transmissionin multiple carriers.

Since the user equipment performs UL transmission in units of subframes,the user equipment may perform UL transmission in the carriers in whichthe transmission is possible at each UL transmission time (e.g., asubframe) regardless of whether the scheduling indicated by the UL grantis a single subframe scheduling or a multi-subframe scheduling.

FIGS. 24 to 27 exemplifies a self-carrier scheduling, but the presentinvention may be applied similarly to the case where the UL grantindicating cat-4 LBT/cat-2 LBT is cross-carrier scheduled from PCellusing licensed band or SCell or is cross-carrier scheduled from LAASCell using unlicensed band. Accordingly, cat-4 LBT or cat-2 LBT may beindicated to the user equipment through self-carrier scheduling, orcat-4 LBT or cat-2 LBT may be indicated to the user equipment throughcross-carrier scheduling. The UL scheduling method is set to one ofself-carrier scheduling or cross-carrier scheduling for each carrier,and the present invention may be applied to a case where differentscheduling methods are applied to each carrier.

Although an LBT gab for performing the LBT between consecutive subframesis not specified and described in FIGS. 25 to 27, the present inventioncan be applied to both cases that LBT gaps are present or not presentbetween subframes.

Embodiment 2: CWS Adjustment for Uplink Multi-Carrier Transmission

As a channel access method for downlink multi-carrier transmission whena plurality of LAA Scell are configured, the type-A and the type-Bexplained in the first embodiment are present.

Type-A has two schemes as a CWS adjustment method. The first scheme(i.e., type A1) manages CWS in each carrier and extracts a BO counterindependently for each carrier according to the scheme used in singlecarrier channel access. The second scheme (i.e., type A2) manages CWS ineach carrier in the same manner as used for the single carrier channelaccess, but sets a common BO counter for multi-carrier transmission. TheBO counter selected from the largest CWS (i.e., the maximum CWp) amongthe CWS of each carrier is set as the common BO counter.

Type-B also has two schemes as a CWS adjustment method. In the firstscheme (i.e., type B1), a carrier set (hereinafter, referred to as a setC) for multi-carrier transmission has a single CWS (hereinafter,referred to as a CWS set C). Based on the HARQ-ACK feedbackcorresponding to the PDSCH transmission in the reference subframetransmitted in all the carriers of the set C, the CWS set C is increasedif the HARQ-ACK values determined as NACK are at least 80% or more, andotherwise it is reset to the minimum value. The second scheme (i.e.,type B2) manages CWS in each carrier according to the scheme used in thesingle carrier channel access, but the BO counter for the carrier (c_j)performing cat-4 LBT for multi-carrier transmission using themulti-carrier type B scheme is set to a BO counter selected from thelargest CWS (i.e., maximum CWp) among the CWS of each carrier. Cat-2 LBT(i.e., Tmc=25 us) occurs in the carrier (c_i) (i≠j) other than thecarrier (c_j) in the type-B method, but the DL transmission alwaysregards cat-4 as the basic LBT. Therefore, even if cat-2 LBT isperformed on the carrier (c_i) in the case of managing the CWS in eachcarrier according to the type B2, the result of the DL transmission inthe carrier is reflected in the corresponding CWS.

Meanwhile, unlike the conventional method, the following method can beconsidered as a CWS adjustment method in the downlink multi-carriertype-B transmission method. The base station performs cat-2 LBT (i.e.,Tmc=25 us) in a carrier (c_i) (i*j) other than the carrier (cj) set toperform cat-4 LBT. In this case, even if the base station always regardscat-4 as the basic LBT in the DL transmission, unlike the conventionaltype B2 scheme, it may not perform the CWS update that increases orresets the CWS according to the transmission from the base station withregard to the carriers not performing the cat-4 LBT. Therefore, when theCWS is managed in each carrier as in the type B2 of the type-B methodand the cat-2 LBT is performed in the carrier (c_i), the result of theDL transmission in the carrier can be prevented from being reflected inthe corresponding CWS. That is, in case of managing the CWS for eachcarrier in the type-B method, the result of the DL transmission in thecarrier in which cat-2 LBT is performed is not reflected in the CWS ofthe corresponding carrier. In this case, only the result of the DLtransmission in the carrier in which cat-4 LBT is performed may bereflected in the CWS of the corresponding carrier. On the other hand, incase of uplink transmission, the base station informs, through the ULgrant, the user equipment of the LBT type to be performed by userequipment when scheduling the PUSCH transmission. The LBT type may be,for example, (i) a Cat-4 LBT (or type 1 channel access), or (ii) a Cat-2LBT (e.g., LBT based on 25 us CCA, or type 2 channel access) that onlyperforms a sensing of a single interval. The user equipment performs LBTaccording to the indicated LBT type and transmits the PUSCH. Therefore,according to the LBT type indication of the base station, there may be acase where the LBT type in all carriers in which the user equipmentperforms uplink transmission (e.g., PUSCH) is not cat-4 LBT. That is,cat-4 LBT may be indicated for some carriers while cat-2 LBT isindicated for other carriers among the carriers that the base intendstransmission to be performed by the user equipment. Therefore, in thechannel access method for uplink multi-carrier transmission, a CWSadjustment method different from that of the downlink assuming only thecat-4 LBT is needed. Hereinafter, an uplink CWS adjustment method in thebase station and the user equipment for UL transmission in case of ULtransmission (e.g., PUSCH) on multiple carriers will be described.

Unlike the downlink multi-carrier transmission method, in the uplinktransmission in which the user equipment performs transmission, cat-4LBT or cat-2 LBT may be dynamically indicated to each carrier at asingle subframe-level or a multi-subframe level through the UL grant.Therefore, the user equipment may be configured to manage a CWS for eachcarrier for uplink multi-carrier transmission. The user equipment maymanage the CWS for each carrier regardless of whether the cat-4 LBT orthe cat-2 LBT is performed for the PUSCH transmission on each carrieraccording to the LBT type indicated by the UL grant for each carrier.Therefore, the terminal is allowed to have a self-defer time, ifnecessary, for each carrier for PUSCH transmission on multiple carrierswhen the base station requests the user equipment to performsimultaneous transmission on multiple carriers or until the time pointat which simultaneous transmission can start within the intervalallowing the LBT if the simultaneous transmission on multiple carriersis requires at the terminal.

As a method for setting a carrier which is allowed to have a self-defertime, the multi-carrier transmission can be performed with having theself-defer time on all the carriers in which the multi-carriertransmission is intended, regardless of the LBT type (e.g., cat-2 LBT,cat-4). Therefore, when the channel sensing in the carrier performingcat-4 LBT ends after the channel sensing period in the carrierperforming cat-2 LBT, a self-defer time may be set for the carrierperforming cat-2 LBT so as to enable multi-carrier transmission.

As another method, the self-defer time may be set only in carriers forwhich cat-4 LBT is indicated, but if it is possible to transmit on allcarriers at the time of transmission regardless of the cat-2 LBT/cat-4LBT setting, the multi-carrier transmission can be performed. Since theLBT interval in the carrier indicated to perform cat-2 LBT isstochastically shorter than the LBT interval in the carrier indicated toperform cat-4 LBT, the multi-carrier transmission can be performed bysetting the self-defer time only in the carriers indicated to performcat-4 LBT.

As a yet another method, the self-defer time may be set only in carriersfor which cat-4 LBT is indicated to perform the multi-carriertransmission consisting only of carriers carrying cat-4. Since the LBTinterval in the carrier indicated to perform cat-2 LBT is stochasticallyshorter than the LBT interval in the carrier indicated to perform cat-4LBT, the multi-carrier transmission can be performed by setting theself-defer time only in the carriers indicated to perform cat-4 LBT. Inaddition, when the channel of one or more carriers performing the cat-4LBT is not idle, the multi-carrier transmission may be enabled at thetransmission possible time of the carrier for which cat-2 LBT isindicated.

Meanwhile, as a method of adjusting CWS to perform cat-4 LBT in downlinkmulti-carrier transmission, a common random backoff (BO) counter can beselected from the CWS of the carrier having the largest CWS in the CWSset managed by each carrier to apply the corresponding BO counter to allthe carriers in which multi-carrier transmission is intended. However,unlike the downlink in which the cat-4 LBT is always performed, sincethe cat-2 LBT or the cat-4 LBT can be performed for each carrier in theuplink, the CWS adjustment method for the carriers for which cat-2 LBTis indicated may be further considered.

First, when a method such as type-A2 for downlink multi-carriertransmission is applied to an uplink, an ambiguity may arise thatwhether the carrier set for selecting the maximum CWS includes a CWSindividually managed in a carrier scheduled to perform cat-2 LBT. Tosolve the problem, the following two methods can be considered. Thefirst method is to select the maximum CWS among CWSs of all carriersscheduled for UL transmission on multiple carriers and extract a commonBO counter N therefrom. Since the cat-4 LBT/cat-2 LBT is dynamically setthrough the UL grant for each carrier and it is configured to manage theCWS for each carrier, even if an LBT type for a specific carrier isindicated as cat-2 LBT, a common backoff counter can be extractedconsidering the CWSs of all carriers in which the multi-carriertransmission is intended. The second method is to select the maximum CWSamong the CWS of the carriers indicated to perform cat-4 LBT among thecarriers scheduled for UL transmission on the multiple carriers andextract a common BO counter N therefrom. Even if the CWS is managed ineach carrier, only CWSs of the carriers in which cat-4 LBT is performedat the current time may be considered. Accordingly, by excluding thepossibility of unnecessarily performing more back-off when the CWS ofcarriers in which cat-2 LBT is performed is larger than the CWS ofcarriers in which cat-4 LBT is performed, it is possible to increase thepossibility of acquiring the channel when the uplink multi-carriertransmission is needed.

As another method, when a method such as type-B2 for downlinkmulti-carrier transmission is applied to an uplink, an ambiguity mayarise that whether the carrier set for selecting the maximum CWSincludes a CWS individually managed in a carrier scheduled to performcat-2 LBT. The following two methods can be considered. The first methodis to select the maximum CWS among CWSs of all carriers scheduled for ULtransmission on multiple carriers and extract a common BO counter N ofthe representative carrier for performing cat-4 LBT therefrom. Since thecat-4 LBT/cat-2 LBT is dynamically set through the UL grant for eachcarrier and it is configured to manage the CWS for each carrier, even ifan LBT type for a specific carrier is indicated as cat-2 LBT, the BOcounter of the representative carrier in which cat-4 LBT is performedcan be extracted considering the CWSs of all carriers in which themulti-carrier transmission is intended. The second method is to selectthe maximum CWS among the CWS of the carriers indicated to perform cat-4LBT among the carriers scheduled for UL transmission on the multiplecarriers and extract a common BO counter N of the representative carrierfor performing cat-4 LBT therefrom. Even if the CWS is managed in eachcarrier, only CWSs of the carriers in which cat-4 LBT is performed atthe current time may be considered. Accordingly, by excluding thepossibility of unnecessarily performing more back-off when the CWS ofcarriers in which cat-2 LBT is performed is larger than the CWS ofcarriers in which cat-4 LBT is performed, it is possible to increase thepossibility of acquiring the channel when the uplink multi-carriertransmission is needed.

In the case of that the type-B scheme used for the downlink is appliedto the uplink multi-carrier transmission (i.e., cat-4 LBT is appliedonly for the representative carrier, and even if cat-4 LBT or cat-2 LBTis signaled, via the UL grant, to other carriers except therepresentative carrier among the carriers in which the multi-carriertransmission is intended, the user equipment performs a channel sensingthrough a T_mc (e.g., 25 us) CCA before the transmission time of thecarrier on which the representative carrier has successfully performedchannel access), when determining the CWS for the next UL transmission,a solution for to whether the CWS should be adjusted byconsidering/reflecting the previous UL transmission (e.g., ULtransmission in which cat-4 LBT or cat-2 LBT is signaled) on thecorresponding carrier. The process of adjusting the CWS can be referredto FIG. 18 and the description thereof.

As a method, when the user equipment performs uplink multi-carriertransmission, regardless of which LBT type is signaled from the basestation or which LBT type is performed for each carrier, the userequipment may perform CWS adjustment for the next UL transmission ofeach carrier by determining ACK, NACK or DTX based on the detection bythe base station for the UL transmission of the corresponding carrier.When a single CWS is managed for multiple carriers, CWS adjustment maybe performed by determining ACK, NACK or DTX for UL transmission in areference subframe for all carriers in which UL transmission isperformed. A method for the user equipment to determine ACK, NACK or DTXfor the corresponding UL transmission and to adjust the CWS may bedetermined based on the value of the NDI transmitted by the UL grant asdescribed in FIG. 18.

As another method, the user equipment may perform CWS adjustment for thenext UL transmission by determining ACK, NACK or DTX based on thedetection by the base station for the UL transmission of thecorresponding carrier only for the UL transmission of the carrier inwhich cat-4 LBT is signaled as an LBT type of the user equipment. Amethod for the user equipment to determine ACK, NACK or DTX for thecorresponding UL transmission and to adjust the CWS may be determinedbased on the value of the NDI transmitted by the UL grant as describedin FIG. 18. Since the carrier configured to perform cat-4 LBT is set bythe base station with expecting the CWS adjustment of the userequipment, the user equipment may perform CWS adjustment even if it hasperformed channel sensing of Tmc=25 us by the type-B and hasparticipated in the multi-carrier transmission. Thus, for the ULtransmission of each carrier, the user equipment may perform CWSadjustment based on the signaled LBT type regardless of the LBT typeactually performed. That is, the user equipment may perform CWSadjustment by determining ACK, NACK or DTX for UL transmission in thereference subframe of the carrier for which cat-4 LBT is signaled. Amethod for the user equipment to determine ACK, NACK or DTX for thecorresponding UL transmission and to adjust the CWS may be determinedbased on the value of the NDI transmitted by the UL grant as describedin FIG. 18.

As a yet another method, the user equipment may perform CWS adjustmentfor the next UL transmission by determining ACK, NACK or DTX based onthe detection by the base station for the UL transmission of thecorresponding carrier only for the UL transmission of the carrier inwhich cat-4 LBT is signaled as an LBT type of the user equipment and inwhich the cat-4 LBT is performed. A method for the user equipment todetermine ACK, NACK or DTX for the corresponding UL transmission and toadjust the CWS may be determined based on the value of the NDItransmitted by the UL grant as described in FIG. 18. Considering thatthe CWS adjustment does not refer to the carriers in which cat-2 LBT isperformed in a single-carrier transmission, it may be difficult toobtain a channel for transmission of the multiple carriers according tothe CWS adjustment method compared to user equipments transmitting LAAUL without multi-carrier transmission. Therefore, the CWS adjustment maybe configured not to be performed for a UL transmission of a carrier inwhich cat-4 LBT has not been actually performed even if it hasparticipated in the multi-carrier transmission.

Next, the operation of the user equipment after an LBT of the precedingsubframe has failed when a multi-subframe scheduling is performed in asingle carrier will be described.

-   -   If there is an LBT gap or a CCA gap for performing LBT between        consecutive subframes scheduled for multi-subframes,        -   When the LBT type is designated as cat-4 LBT in the UL grant            for multi-subframe scheduling, or when the LBT type is            designated as cat-4 LBT in the UL grant scheduling each            subframe in the multi-subframe, if the LBT of the preceding            subframe has failed, it is configured that a new BO counter            for transmission to the later UL subframe is obtained, and            follow the uplink channel access procedure.        -   When the LBT type is designated as cat-4 LBT in the UL grant            for multi-subframe scheduling, or when the LBT type is            designated as cat-4 LBT in the UL grant scheduling each            subframe in the multi-subframe, if the LBT of the preceding            subframe has failed, it is configured that the preceding BO            counter resumes and to follow the uplink channel access            procedure.    -   If there is no LBT gap or CCA gap for performing LBT between        consecutive subframes scheduled for multi-subframes,        -   When the LBT type is designated as cat-4 LBT in the UL grant            for multi-subframe scheduling, or when the LBT type is            designated as cat-4 LBT in the UL grant scheduling each            subframe in the multi-subframe, it is configured that BO            counter after the failure of the LBT of the preceding            subframe resumes and to follow the uplink channel access            procedure.

Next, the operation of the user equipment after an LBT of the precedingsubframe has failed when a multi-subframe scheduling is performed onmultiple carriers will be described. If the multi-subframe scheduling isscheduled to have no gap between subframes in at least one carrier,uplink transmission may not always be possible in other carriers thathave failed LBT due to the consecutive transmission in that carrier. Inorder to solve this problem, when the user equipment is scheduled formultiple carriers and is subjected to multi-subframe scheduling so thatthere is no gap between subframes for a specific carrier, the userequipment may be configured to give an arbitrary gap within themulti-subframe of the corresponding carrier. Accordingly, the othercarrier in which the preceding LBT has failed and the carrier(s)succeeding in the current LBT can simultaneously perform multi-carriertransmission.

Embodiment 3: Channel Access for Uplink Multi-Subframe Transmission

Some subframes of consecutive subframe(s) may be dropped by the userequipment for some reason when the transmission of consecutivesubframe(s) on the LAA SCell is scheduled. Here, dropping a subframemeans that UL transmission (e.g., PUSCH) is stopped/dropped in asubframe. That is, the UL transmission in the consecutive subframe(s)can be suspended/stopped before completed. For example, if the userequipment is in a power limitation case, the UL transmission may bedropped in some subframes according to power scaling rules. Thereby,unlike intention of the base station, UL transmission may be performedin non-consecutive subframe(s).

Hereinafter, a channel access procedure when a UL transmission innon-consecutive subframe(s) is performed due to dropping of somesubframes while transmission of consecutive subframe(s) is scheduledwill be described. For the sake of understanding, the present inventionexemplifies a power limitation case of a user equipment as a case wherea subframe is dropped. However, the present invention can be applied,without limitation, to the channel access procedure in the case whereconsecutive subframe(s) are scheduled but a UL transmission is performedin non-consecutive subframe(s).

For reference, in accordance with section 5.1.1.1 of 3GPP TS 36.213v13.2.0, the following rules are used in the power scaling operation ofthe user equipment in the power limitation scenario of the userequipment: if the secondary cell group (SCG) is not configured and thetotal transmission power exceeds the power allowable limitation value ofthe user equipment, the user equipment allocates the transmission powerby prioritizing the transmission of the PUCCH or by prioritizing thetransmission of the PUSCH including the UCI, and equally distributes theremaining transmission power to the PUSCH transmitted on the remainingscheduled carriers. The transmission power of the user equipment isdetermined as a subframe-by-subframe.

In the case of the LAA SCell, the base station may allocate consecutivesubframes (hereinafter, referred to as UL burst) to the user equipment,and the user equipment performs one of cat-4 LBT and cat-2 LBT accordingto the LBT type signaled immediately before the transmission of the ULburst, and transmit the corresponding UL burst when the LBT issuccessful. Here, if the UL burst is scheduled without a gap betweensubframes, and the LBT succeeds at the start of the UL transmissionburst, transmission of the UL transmission burst may be performedwithout additional LBT. However, when the user equipment is in a powerlimitation state, a specific subframe of the LAA SCell may be droppeddue to the UL transmission of the licensed cell according to the powerscaling operation. For this reason, a gap may occur in the UL burst.

FIG. 28 illustrates a case where one subframe is dropped on the LAASCell.

Referring to FIG. 28, four consecutive UL subframes are scheduled on theLAA SCell. However, in the power limitation state of the user equipment,priority is given to the power of the UL SF #(n+1) of the licensed cell,the UL subframe in the UL SF #(n+1) of the LAA SCell may be dropped. Inthis case, a user equipment may intend to perform data transmission oncontiguous UL subframes after the success of the UL LBT on the LAASCell. However, there may be an ambiguity on whether to performtransmissions on the UL #(n+2) and UL SF #(n+3) without LBT, anambiguity on which LBT type should be performed, and an ambiguity onwhich LBT parameters should be used if cat-4 LBT is to be performed.Therefore, the present invention provides a solution for the case asbelow.

First, a case where the cat-2 LBT is configured to be performed at thestart of the UL transmission burst for the UL transmission on the LAAScell will be described.

-   -   If only the 25 us LBT is performed immediately before the SF        #(n+2) transmission on the LAA SCell and the LBT is successful        (i.e., if the channel is continuously idle or if the channel is        continuously idle and the 25 us LBT succeeds), UL data        transmission can be performed in UL SF #(n+2) and UL SF #(n+3).        If the 25 us LBT fails, the following two methods can be        considered.        -   As a first method, if the 25 us LBT is continuously            performed and the LBT succeeds, transmission can be            performed in UL SF #(n+3). In this case, if the 25 us LBT            succeeds in the UL SF #(n+2), the UL transmission is started            after the LBT success time but the CP of the next symbol            that is, SF #(n+3) may be extended in order to occupy a            portion of the UL SF #(n+2) after the LBT success.        -   As a second method, in order to transmit UL data in UL SF            #(n+3), cat-4 LBT may be performed from UL SF #(n+2). In            this case, the cat-4 LBT may be performed by setting the LBT            parameter based on the LBT priority class 1 having the            highest priority among the priority class.        -   As another method, the base station may designate an LBT            priority class together with an LBT type indication via a UL            grant, and the user equipment may perform cat-4 LBT by            setting an LBT parameter based on the designated LBT            priority class. However, since the UL transmission burst is            configured to perform cat-2 LBT when receiving initial            signaling from the base station, even if the cat-4 LBT is            performed for transmission of the remaining subframes, the            corresponding cat-4 LBT may not be reflected in the CWS            adjustment. Alternatively, the cat-4 LBT in the SF #(n+2)            performed by the user equipment may be applied/reflected in            the CWS adjustment when the cat-4 LBT UL scheduling is            received after the next 4 ms (e.g., SF #(n+2) is set as a            reference subframe).

Next, a case where the cat-4 LBT is configured to be performed at thestart of the UL transmission burst for the UL transmission on the LAAScell will be described.

-   -   As an embodiment, if cat-4 LBT is completed before the SF #(n+2)        transmission on LAA SCell by setting cat-4 LBT to be performed        from SF #(n+1) on LAA SCell, the UL data transmission scheduled        in the UL SF #(n+2) and the UL SF #(n+3) may be performed. If        the cat-4 LBT is not completed before the SF #(n+2) transmission        on the LAA SCell, the cat-4 LBT may continue until the SF #(n+3)        transmission on the LAA SCell. The Random backoff counter being        used for cat-4 LBT may be continuously used.    -   As another embodiment, if only the 25 us LBT is performed        immediately before the SF #(n+2) transmission on the LAA SCell        and the cat-2 LBT is successful (i.e., if the channel is        continuously idle or if the channel is continuously idle and the        25 us LBT succeeds), UL data transmission can be performed in UL        SF #(n+2) and UL SF #(n+3). Here, if the 25 us LBT fails, the        following two methods can be considered.        -   As a first method, if the 25 us LBT is continuously            performed and the LBT succeeds, transmission can be            performed in UL SF #(n+3). In this case, if the 25 us LBT            succeeds in the UL SF #(n+2), the UL transmission starts            after the LBT success time but the CP of the next symbol            that is, SF #(n+3) may be extended in order to occupy a            portion of the UL SF #(n+2) after the LBT success.        -   As a second method, in order to transmit UL data in UL SF            #(n+3), cat-4 LBT may be performed from UL SF #(n+2). In            this case, the cat-4 LBT may be performed by setting the LBT            parameter based on the LBT priority class 1 having the            highest priority among the priority class.        -   As another method, the base station may designate an LBT            priority class together with an LBT type indication via a UL            grant, and the user equipment may perform cat-4 LBT by            setting an LBT parameter based on the designated LBT            priority class. In this regard, since the UL transmission            burst is configured to perform cat-4 LBT when the initial            signaling is received from the base station, even if the            cat-4 LBT is performed for transmission of the remaining            subframes, the corresponding cat-4 LBT may not be reflected            in the CWS adjustment. In this regard, since the UL            transmission burst is configured to perform cat-4 LBT when            receiving initial signaling from the base station, the CWS            adjustment may be performed by regarding the transmission            start time (e.g., UL SF # n in FIG. 28) of the UL            transmission burst as a reference subframe. Also, each UL            transmission burst can be regarded as a different UL burst            from the viewpoint that a single UL transmission burst is            split and different cat-4 LBTs are performed. Accordingly,            the cat-4 LBT in the SF #(n+2) or SF #(n+3) performed by the            user equipment may be applied/reflected in the CWS            adjustment when the cat-4 LBT UL scheduling is received            after the next 4 ms (e.g., SF #(n+2) or SF #(n+3) is set as            a reference subframe).

Alternatively, the following operation may be considered, regardless ofwhether it is configured to perform cat-4 LBT or cat-2 LBT at thebeginning of the UL transmission burst for UL transmission on the LAASCell. Specifically, if a specific subframe is not transmitted (i.e.,the UL transmission is stopped) in consecutive UL subframe scheduling ofa specific LAA SCell (e.g., due to a power limitation case between alicensed carrier and a LAA SCell), then a contiguous 25 us LBT may beperformed (from the time point when the UL transmission is stopped) fora transmission of the later UL subframe, and transmit the later ULsubframe (e.g., UL SF #(n+2) in FIG. 28) if the channel is idle. Inaddition, when the channel is not idle at the time of performing thecontiguous 25 us LBT (from the time point when the UL transmission isstopped), the user equipment may perform cat-4 LBT, and transmit thelater subframe (e.g., UL SF #(n+2) in FIG. 28) if the LBT succeeds.Here, the LBT parameter used in the cat-4 LBT may be configured inconsideration of the LBT priority class indicated by the UL grant. Also,the UL grant refers to a UL grant that schedules the UL subframe beingtransmitted. Depending on the scheduling scheme, the UL grant may be aUL grant scheduling a multi-subframe, or may be a UL grant thatindividually schedules each subframe in a multi-subframe.

Here, performing the contiguous 25 us LBT is to check if the channel iscontinuously idle. Considering that the LBT should be performed at thetime of UL transmission, the above method can be generalized as follows.

If a specific subframe is not transmitted in the contiguous UL subframescheduling of the LAA SCell (i.e., the UL transmission isstopped/suspended during a consecutive UL subframe transmission),

-   -   If the channel is continuously idle starting from the time point        when the UL transmission is stopped (until the LBT point for the        UL subframe), the user equipment may perform 25 us LBT (i.e.,        cat-2 LBT) for transmission of the later subframe (i.e., the        remaining UL subframe),    -   If the channel is not continuously idle starting from the time        point when the UL transmission is stopped (until the LBT point        for the UL subframe), the user equipment may perform cat-4 LBT        for transmission of the later subframe (i.e., the remaining UL        subframe). The cat-4 LBT may be performed considering the LBT        priority class indicated in the UL grant.

If the LBT succeeds according to the above procedure, the user equipmentcan resume transmission of the later UL subframe (i.e., the remaining ULsubframe). On the other hand, if the LBT fails, since the channel is notidle, the user equipment may additionally perform cat-4 LBT fortransmission of the later UL subframe (e.g., UL SF #(n+3) in FIG. 28).

On the other hand, in the case of multi-carrier transmission withmultiple LAA SCells, for UL transmission,

(UL multi-carrier (MC) LBT type 1) an independent LBT is performed totransmit the UL subframe for each LAA SCell corresponding to the LAASCell, and the UL transmission is performed through an LAA SCell carrierthat succeeds the LBT, or

(UL MC LBT type 2) cat-4 LBT is performed on a specific carrier(hereinafter, referred to as a designated carrier) with regard tosubframes in which cat-4 LBT is performed among one or more LAA SCellcarriers, and the UL multi-carrier transmission through multiplecarriers is performed when the channel is detected to be idle byperforming 25 us LBT immediately before the transmission on othercarriers for the subframe transmission. One carrier uniformly randomlyselected from the carriers scheduled to perform cat-4 LBT is used as thedesignated carrier.

The UL MC LBT type 2 may be performed within a specific carrier set. Forexample, if UL grants are received in a carrier set that has the samestart time in a subframe and is scheduled with a cat-4 LBT, the userequipment may perform 25 us LBT immediately before transmission onanother carrier in a carrier set if the cat-4 LBT in the specifiedcarrier in the carrier set has been successfully completed. Thecorresponding carrier set may be set in consideration of regulation ofeach country. For example, in Europe, a part/whole carrier of acorresponding channel bonding may be set as one carrier set consideringchannelization at 5 GHz. Further, a UL subframe in which cat-2 LBT ULgrant is configured may be transmitted by independently performing 25 usLBT without participating in the MC LBT in the corresponding carrierset. In addition, even if the cat-4 LBT of the designated carrier amongsubframes for which cat-4 LBT is configured fails, the UL transmissionof the carrier that has received the UL grant with cat-2 LBT may beperformed independently.

In addition, when transmitting through a plurality of LAA SCellcarriers, the MCOT which is set in a specific carrier may be shared by aplurality of carriers as follows. Further, the corresponding MCOT may beconfigured to start from channel occupancy in a carrier performing cat-4LBT.

-   -   A base station that initiates a DL transmission based on a type        B multi-carrier LBT that obtains an MCOT may share channel        occupancy with a user equipment on all carriers that have        completed the type B LBT.    -   The channel occupancy may be started using DL transmission after        the carrier performing cat-4 LBT completes the cat-4 LBT,

On the other hand, when it is configured to perform cat-4 LBT as the LBTtype at the start time of the UL transmission burst for UL transmissionon the LAA SCell, the following two methods may be considered.

-   -   As a method, if cat-4 LBT is completed before the SF #(n+2)        transmission on LAA SCell by setting cat-4 LBT to be performed        from SF #(n+1) on LAA SCell, the UL data transmission scheduled        in the UL SF #(n+2) and the UL SF #(n+3) may be performed. If        the cat-4 LBT is not completed before the SF #(n+2) transmission        on the LAA SCell, the cat-4 LBT may be performed until the SF        #(n+3) transmission on the LAA SCell.    -   As another method, if only the 25 us LBT is performed        immediately before the SF #(n+2) transmission on the LAA SCell        and the cat-2 LBT is successful, UL data transmission can be        performed in UL SF #(n+2) and UL SF #(n+3). Here, if the 25 us        LBT fails, the following two methods can be considered.        -   As a first method, if the 25 us LBT is continuously            performed and the LBT succeeds, transmission can be            performed in UL SF #(n+3). In this case, if the 25 us LBT            succeeds in the UL SF #(n+2), the UL transmission is            configured to start after the LBT success time but the CP of            the next symbol that is, SF #(n+3) may be extended in order            to occupy a portion of the UL SF #(n+2) after the LBT            success.

In a process of (consecutive) UL subframe transmissions in LAA SCellcarriers to be transmitted by multiple carriers, it may be impossible totransmit a specific subframe along with implementing a power scalingoperation in a power limitation state for transmission of a licensedcarrier. When a transmission of a subframe (e.g., UL SF #(n+1)) of aplurality of LAA SCell carriers becomes impossible due to transmissionof the licensed carrier as shown in FIG. 29, it is necessary to performadditional LBT as described above for a transmission of the latersubframe (e.g., UL SF #(n+2)) of the LAA SCell carrier. However, thereare a variety of LBT procedures for the multi-carrier transmission(e.g., UL MC LBT type 1 or UL MC LBT type 2), and the LBT procedure forUL subframe transmission should be determined after the subframe inwhich transmission is dropped according to each MC LBT procedure.

-   -   In the case of performing independent UL LBT (e.g., UL MC LBT        type 1) for each LAA SCell carrier, the later UL subframe        transmission may be performed through an additional LBT in a UL        subframe in which transmission is dropped as follows.        -   As in the UL MC LBT type 1, an LAA SCell LBT (e.g., cat-4 or            25 us LBT) may be implemented independently for each            carrier. In this case, if the UL transmission is not            performed in the UL SF #(n+1) for each LAA SCell carrier,            the 25 us LBT may be performed for the UL SF #(n+2)            transmission, and the UL transmission may be performed in a            carrier in which the channel is idle. In a carrier in which            the channel is not idle, an additional cat-4 LBT may be            performed (in this case, consider the LBT priority class            defined in the UL grant or select the priority class            described above), and the UL transmission is possible in the            later UL subframe if the channel is idle.        -   Even if the LAA SCell LBT is implemented independently for            each carrier as in the UL MC LBT type 1, if a subframe to be            dropped occurs as in the UL SF #(n+1), 25 us LBT may be            performed independently for each carrier. In this regard, if            a carrier in which the channel is not idle occurs, a            specific carrier may be selected and cat-4 LBT may be            performed on the selected carrier. Further, only 25 us LBT            may be performed on other carriers (including the remaining            carrier in which the channel is not idle), and whether to            perform the later UL subframe transmission may be determined            for each carrier.        -   In the subframe configured to perform 25 us LBT through UL            grant according to the above described process, by            performing only the 25 us LBT without the cat-4 LBT            procedure, the UL transmission may be performed in the later            subframe (e.g., UL SF #(n+2)) after the subframe in which            the transmission is dropped. Further, when the cat-4 LBT is            only performed on a specific carrier and the 25 us LBT is            performed on other carriers, it is also possible to            participate in the simultaneous transmission on the subframe            for which 25 us LBT is configured through the UL grant.    -   In the case of a UL multi-carrier transmission scheme, such as        UL MC LBT type 2, where cat-4 LBT is performed based on a        specific designated carrier in an LAA SCell and 25 us LBT is        performed on other carriers in which cat-4 LBT UL grant is        received for subframe transmission, the following method can be        considered as an additional LBT scheme for UL subframe        transmission after the UL subframe (e.g., UL SF #(n+1)) in which        transmission is dropped.        -   In the case of the UL subframe in which cat-4 LBT UL grant            is received as in the UL MC LBT type 2, if a UL subframe in            which a transmission is dropped occurs before completed            occurs, 25 us LBT is performed for each carrier for the            later UL subframe transmission and the later UL subframe            transmission is possible in the carrier in which the channel            is idle. For carriers in which the channel is not idle, an            additional cat-4 LBT is performed, and UL subframe            transmission is possible if the channel is idle.        -   In the case of the UL subframe in which cat-4 LBT UL grant            is received as in the UL MC LBT type 2, if a UL subframe in            which a transmission is dropped occurs before completed            occurs, a designated carrier may be additionally set (or the            previous defined designated carrier may be reused) for the            later UL subframe transmission. Then, an LBT similar to UL            MC LBT type 2 is performed by performing 25 us LBT on other            carriers and cat-4 LBT on the designated carrier, and then            whether to perform the transmission may be determined for            each carrier in the later UL subframe after the UL subframe            in which the transmission is dropped. In this regard, 25 us            LBT may be performed before setting the designated carrier            for the cat-4 LBT, and adding the designated carrier may be            performed on a carrier in which the channel is not idle at            that time.        -   In the case of the UL subframe in which cat-4 LBT UL grant            is received as in the UL MC LBT type 2, if a UL subframe in            which a transmission is dropped occurs before completed            occurs, only 25 us LBT may be performed for the later UL            subframe transmission. That is, it is also possible to            transmit the later UL subframe only on the carrier in which            the channel is idle for 25 us, and perform the transmission            only checking 25 us immediately before the UL subframe            (e.g., UL SF #(n+2)) transmission which is immediately            followed.        -   When performing the additional cat-4 LBT or 25 us LBT as            described above, it can be performed on the carrier for            which cat-4 LBT is assigned through UL grant. Meanwhile, in            case of UL subframe for which 25 us LBT is configured            through UL grant, if additional LBT is performed due to            transmission drop, the later UL subframe transmission may be            performed considering the success of independent 25 us LBT.            However, in order to perform the simultaneous MC            transmission by the user equipment, an operation similar            with that in the subframe in which cat-4 LBT UL grant is            configured by participating in an additional cat-4 LBT or 25            us LBT.

For the UL subframe transmission after the subframe in which atransmission is dropped, in case of the carrier transmission in which 25us LBT (including cat-4 LBT) succeeded for the additional LBT schemeproposed above, it is possible to transmit a signal for channelreservation by expanding the CP by copying the signal transmitted fromthe OFDM symbol with the CP extension.

FIG. 30 illustrates configurations of a user equipment and a basestation according to an exemplary embodiment of the present invention.In the present invention, the user equipment may be implemented byvarious types of wireless communication devices or computing devices ofwhich portability and mobility are guaranteed. The user equipment (UE)may be referred to as terminal, a station (STA), a mobile subscriber(MS), and the like. In the present invention, the base station maycontrol and take charge of cells (e.g., a macro cell, a femto cell, apico cell, and the like) corresponding to service areas and performfunctions including signal transmission, channel designation, channelmonitoring, self diagnosis, relay, and the like. The base station may bereferred to as an evolved NodeB (eNB), an access point (AP), and thelike.

Referring to FIG. 30, the user equipment 100 may include a processor110, a communication module 120, a memory 130, a user interface unit140, and a display unit 150.

The processor 110 may execute various commands or programs according tothe present invention and process data in the user equipment 100.Further, the processor 100 may control all operations of the respectiveunits of the user equipment 100 and control data transmission/receptionamong the units. For example, the processor 110 may perform DL/ULtransmission/reception in an LTE-U cell in an LAA environment. Indetail, the processor 110 may perform aforementioned various operations,for example, DL/UL transmission/reception, verification of an HARQ-ACKfeedback set, CWS adjustment, and the like.

The communication module 120 may be an integrated module that performsmobile communication using a mobile communication network and wirelessLAN access using a wireless LAN. To this end, the communication module120 may include a plurality of network interface cards such as cellularcommunication interface cards 121 and 122 and a wireless LAN interfacecard 123 in an internal or external type. In FIG. 30, the communicationmodule 120 is illustrated as the integrated module, but the respectivenetwork interface cards may be independently disposed according to acircuit configuration or a purpose unlike FIG. 30.

The cellular communication interface card 121 transmits/receives a radiosignal to/from at least one of a base station 200, an external device,and a server by using the mobile communication network and provides acellular communication service at a first frequency band based on acommand of the processor 110. The cellular communication interface card121 may include at least one NIC module using an LTE-licensed frequencyband. The cellular communication interface card 122 transmits/receivesthe radio signal to/from at least one of the base station 200, theexternal device, and the server by using the mobile communicationnetwork and provides the cellular communication service at a secondfrequency band based on the command of the processor 110. The cellularcommunication interface card 122 may include at least one NIC moduleusing an LTE-unlicensed frequency band. For example, the LTE-unlicensedfrequency band may be a band of 2.4 GHz or 5 GHz.

The wireless LAN interface card 123 transmits/receives the radio signalto/from at least one of the base station 200, the external device, andthe server through wireless LAN access and provides a wireless LANservice at the second frequency band based on the command of theprocessor 110. The wireless LAN interface card 123 may include at leastone NIC module using a wireless LAN frequency band. For example, thewireless LAN frequency band may be an unlicensed radio band such as theband of 2.4 GHz or 5 GHz.

The memory 130 stores a control program used in the user equipment 100and various resulting data. The control program may include a programrequired for the user equipment 100 to perform wireless communicationwith at least one of the base station 200, the external device, and theserver. The user interface 140 includes various types of input/outputmeans provided in the user equipment 100. The display unit 150 outputsvarious images on a display screen.

Further, the base station 200 according to the exemplary embodiment ofthe present invention may include a processor 210, a communicationmodule 220, and a memory 230.

The processor 210 may execute various commands or programs according tothe present invention and process data in the base station 200. Further,the processor 210 may control all operations of the respective units ofthe base station 200 and control data transmission/reception among theunits. For example, the processor 210 may perform DL/ULtransmission/reception based on LBT in an LAA environment. In detail,the processor 210 may perform aforementioned various operations, forexample, DL/UL transmission/reception, verification of an HARQ-ACKfeedback set, CWS adjustment, and the like.

The communication module 220 may be an integrated module that performsthe mobile communication using the mobile communication network and thewireless LAN access using the wireless LAN like the communication module120 of the user equipment 100. To this end, the communication module 120may include a plurality of network interface cards such as cellularcommunication interface cards 221 and 222 and a wireless LAN interfacecard 223 in the internal or external type. In FIG. 25, the communicationmodule 220 is illustrated as the integrated module, but the respectivenetwork interface cards may be independently disposed according to thecircuit configuration or the purpose unlike FIG. 25.

The cellular communication interface card 221 transmits/receives theradio signal to/from at least one of the user equipment 100, theexternal device, and the server by using the mobile communicationnetwork and provides the cellular communication service at the firstfrequency band based on a command of the processor 210. The cellularcommunication interface card 221 may include at least one NIC moduleusing the LTE-licensed frequency band. The cellular communicationinterface card 222 transmits/receives the radio signal to/from at leastone of the user equipment 100, the external device, and the server byusing the mobile communication network and provides the cellularcommunication service at the second frequency band based on the commandof the processor 210. The cellular communication interface card 222 mayinclude at least one NIC module using the LTE-unlicensed frequency band.The LTE-unlicensed frequency band may be the band of 2.4 GHz or 5 GHz.

The wireless LAN interface card 223 transmits/receives the radio signalto/from at least one of the user equipment 100, the external device, andthe server through the wireless LAN access and provides the wireless LANservice at the second frequency band based on the command of theprocessor 210. The wireless LAN interface card 223 may include at leastone NIC module using the wireless LAN frequency band. For example, thewireless LAN frequency band may be the unlicensed radio band such as theband of 2.4 GHz or 5 GHz.

In FIG. 25, blocks of the user equipment and the base station logicallydivide and illustrate elements of the device. The elements of the devicemay be mounted as one chip or a plurality of chips according to designof the device. Further, some components of the user equipment 100, thatis to say, the user interface 140 and the display unit 150 may beselectively provided in the user equipment 100. Further, some componentsof the base station 200, that is to say, the wireless LAN interface 223,and the like may be selectively provided in the base station 200. Theuser interface 140 and the display unit 150 may be additionally providedin the base station 200 as necessary.

The method and the system of the present invention are described inassociation with the specific embodiments, but some or all of thecomponents and operations of the present invention may be implemented byusing a computer system having a universal hardware architecture.

The description of the present invention is used for illustration andthose skilled in the art will understand that the present invention canbe easily modified to other detailed forms without changing thetechnical spirit or an essential feature thereof. Therefore, theaforementioned exemplary embodiments are all illustrative in all aspectsand are not limited. For example, each component described as a singletype may be implemented to be distributed and similarly, componentsdescribed to be distributed may also be implemented in a combined form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is usable in various communication devices (e.g.,a station or access point using unlicensed band communication, a stationor a base station using cellular communication, or the like) used in awireless communication system.

1. A method for performing uplink transmission in a specific cell by auser equipment in a wireless communication system, the methodcomprising: receiving uplink scheduling information; and when the userequipment has stopped an uplink transmission during the uplinktransmission being performed according to the uplink schedulinginformation, to resume the uplink transmission, performing a second typechannel access when a channel sensed by the user equipment iscontinuously idle after the uplink transmission has been stopped, andperforming a first type channel access when the channel sensed by theuser equipment is not continuously idle after the uplink transmissionhas been stopped, wherein the first type channel access comprisesperforming a random backoff after a channel sensing, and the second typechannel access only comprises performing a channel sensing.
 2. Themethod according to claim 1, wherein the uplink transmission comprises atransmission on a plurality of subframes, and wherein stopping, by theuser equipment, the uplink transmission during the uplink transmissionbeing performed comprises dropping the uplink transmission in a subframeother than a last subframe on the plurality of subframes.
 3. The methodaccording to claim 1, wherein the wireless communication systemcomprises a 3rd generation partnership project (3GPP)-based wirelesscommunication system, and wherein the first type channel accesscomprises a category-4 listen-before-talk (LBT) and the second typechannel access comprises a category-2 LBT.
 4. The method according toclaim 1, wherein the first type channel access comprises performing therandom backoff using a variable size contention window (CW), and whereinthe second type channel access comprises performing the channel sensingfor a duration of 25 us without a random backoff.
 5. The methodaccording to claim 1, wherein the specific cell is an unlicensed cell.6. A user equipment used in a wireless communication system, the userequipment comprising: a wireless communication module; and a processor,wherein the processor is configured to: receive uplink schedulinginformation, and when the user equipment has stopped an uplinktransmission during the uplink transmission being performed according tothe uplink scheduling information, to resume the uplink transmission,perform a second type channel access when a channel sensed by the userequipment is continuously idle after the uplink transmission has beenstopped, and perform a first type channel access when the channel sensedby the user equipment is not continuously idle after the uplinktransmission has been stopped, wherein the first type channel accesscomprises performing a random backoff after a channel sensing, and thesecond type channel access only comprises performing a channel sensing.7. The user equipment according to claim 6, wherein the uplinktransmission comprises a transmission on a plurality of subframes, andwherein stopping, by the user equipment, the uplink transmission duringthe uplink transmission being performed comprises dropping the uplinktransmission in a subframe other than a last subframe on the pluralityof subframes.
 8. The user equipment according to claim 6, wherein thewireless communication system comprises a 3rd generation partnershipproject (3GPP)-based wireless communication system, and wherein thefirst type channel access comprises a category-4 listen-before-talk(LBT) and the second type channel access comprises a category-2 LBT. 9.The user equipment according to claim 6, wherein the first type channelaccess comprises performing the random backoff using a variable sizecontention window (CW), and wherein the second type channel accesscomprises performing the channel sensing for a duration of 25 us withouta random backoff.
 10. The user equipment according to claim 6, whereinthe specific cell is an unlicensed cell.